/* ======================================================================
   Java Prep — styles
   Sections: tokens · base · chrome (topbar/sidebar/toc) · content · components
             · animations · responsive · print
   ====================================================================== */

/* ================= Tokens ================= */
:root {
  --sans: "Inter", ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --mono: "JetBrains Mono", "Fira Code", "Cascadia Code", ui-monospace, Menlo, Consolas, monospace;
  --radius: 14px;
  --radius-sm: 9px;
  --topbar: 60px;
  --sidebar: 300px;
  --toc: 240px;
  --ease: cubic-bezier(0.22, 1, 0.36, 1);
  --spring: cubic-bezier(0.34, 1.56, 0.64, 1);
  --safe-b: env(safe-area-inset-bottom, 0px);
}
[data-theme="dark"] {
  color-scheme: dark;
  --bg: #0b1018;
  --bg-2: #0f1520;
  --panel: #141c29;
  --panel-2: #1a2333;
  --line: #243046;
  --line-2: #2f3d57;
  --ink: #e8edf5;
  --muted: #a3afc2;
  --faint: #6f7c90;
  --accent: #f59e4b;      /* java orange */
  --accent-2: #5aa9ff;    /* spring-ish blue */
  --green: #3fcf6b;
  --red: #ff6b6b;
  --yellow: #e3b341;
  --violet: #b493ff;
  --code-bg: #0a0e15;
  --code-head: #111827;
  --code-line: #1c2636;
  --shadow: 0 12px 34px rgba(0, 0, 0, 0.38);
  --glow: 0 0 0 1px rgba(245, 158, 75, 0.25), 0 10px 30px rgba(245, 158, 75, 0.12);
}
[data-theme="light"] {
  color-scheme: light;
  --bg: #f6f7fb;
  --bg-2: #eef1f6;
  --panel: #ffffff;
  --panel-2: #f2f4f8;
  --line: #dde3ec;
  --line-2: #c9d2df;
  --ink: #18202d;
  --muted: #47546a;
  --faint: #7a8699;
  --accent: #d0590d;
  --accent-2: #1f6feb;
  --green: #1a8a3d;
  --red: #d1242f;
  --yellow: #9a6700;
  --violet: #7c4ddb;
  --code-bg: #0f1520;
  --code-head: #151d2b;
  --code-line: #1c2636;
  --shadow: 0 12px 30px rgba(24, 34, 54, 0.1);
  --glow: 0 0 0 1px rgba(208, 89, 13, 0.25), 0 10px 30px rgba(208, 89, 13, 0.1);
}

/* ================= Base ================= */
*, *::before, *::after { box-sizing: border-box; }
html { scroll-padding-top: calc(var(--topbar) + 16px); -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  font: 16px/1.7 var(--sans);
  color: var(--ink);
  background:
    radial-gradient(1200px 600px at 85% -10%, color-mix(in srgb, var(--accent-2) 9%, transparent), transparent 60%),
    radial-gradient(900px 500px at -10% 110%, color-mix(in srgb, var(--accent) 7%, transparent), transparent 60%),
    var(--bg);
  background-attachment: fixed;
  transition: background-color 0.4s, color 0.4s;
  overflow-x: hidden;
}
a { color: var(--accent-2); text-decoration: none; text-underline-offset: 3px; }
a:hover { text-decoration: underline; }
code, kbd, pre { font-family: var(--mono); font-variant-ligatures: none; }
:not(pre) > code {
  font-size: 0.86em;
  background: var(--panel-2);
  border: 1px solid var(--line);
  padding: 0.06em 0.36em;
  border-radius: 6px;
  overflow-wrap: anywhere;
}
kbd {
  font-size: 0.74em;
  border: 1px solid var(--line-2);
  border-bottom-width: 2px;
  border-radius: 5px;
  padding: 0 5px;
  background: var(--panel);
  color: var(--muted);
}
::selection { background: color-mix(in srgb, var(--accent) 35%, transparent); }
:focus-visible { outline: 2px solid var(--accent-2); outline-offset: 2px; border-radius: 6px; }
img, svg { max-width: 100%; }
.skip-link { position: absolute; left: -999px; top: 8px; z-index: 100; background: var(--accent); color: #fff; padding: 6px 12px; border-radius: 8px; }
.skip-link:focus { left: 8px; }

/* scrollbars */
* { scrollbar-width: thin; scrollbar-color: var(--line-2) transparent; }
*::-webkit-scrollbar { width: 9px; height: 9px; }
*::-webkit-scrollbar-thumb { background: var(--line-2); border-radius: 9px; border: 2px solid transparent; background-clip: padding-box; }

/* ================= Top bar ================= */
.read-progress {
  position: fixed; inset: 0 0 auto 0; height: 3px; z-index: 50;
  background: linear-gradient(90deg, var(--accent), var(--violet), var(--accent-2));
  transform-origin: 0 50%; transform: scaleX(0);
}
.topbar {
  position: fixed; inset: 0 0 auto 0; height: var(--topbar);
  display: flex; align-items: center; gap: 12px; padding: 0 18px;
  background: color-mix(in srgb, var(--bg) 72%, transparent);
  backdrop-filter: saturate(160%) blur(14px);
  -webkit-backdrop-filter: saturate(160%) blur(14px);
  border-bottom: 1px solid transparent;
  z-index: 40;
  transition: border-color 0.3s, box-shadow 0.3s;
}
body.scrolled .topbar { border-bottom-color: var(--line); box-shadow: 0 6px 20px rgba(0, 0, 0, 0.12); }
.brand { display: flex; align-items: center; gap: 7px; font-weight: 800; font-size: 1.08rem; color: var(--ink); letter-spacing: -0.2px; white-space: nowrap; }
.brand:hover { text-decoration: none; }
.brand small { color: var(--faint); font-weight: 600; }
.brand-cup { display: inline-block; transition: transform 0.5s var(--spring); }
.brand:hover .brand-cup { transform: rotate(-16deg) scale(1.2); }
.topbar-right { margin-left: auto; display: flex; align-items: center; gap: 14px; }
.kbd-hint { color: var(--faint); font-size: 0.78rem; white-space: nowrap; }
.icon-btn {
  display: grid; place-items: center; flex: none;
  border: 1px solid var(--line); background: var(--panel); color: var(--ink);
  width: 40px; height: 40px; border-radius: 11px; cursor: pointer;
  transition: transform 0.25s var(--spring), border-color 0.2s, background 0.2s;
}
.icon-btn:hover { transform: translateY(-1px); border-color: var(--accent); }
.icon-btn:active { transform: scale(0.94); }
#menu-btn { display: none; }
.burger { display: grid; gap: 4px; width: 18px; }
.burger i { display: block; height: 2px; border-radius: 2px; background: currentColor; transition: transform 0.35s var(--ease), opacity 0.2s; }
body.nav-open .burger i:nth-child(1) { transform: translateY(6px) rotate(45deg); }
body.nav-open .burger i:nth-child(2) { opacity: 0; }
body.nav-open .burger i:nth-child(3) { transform: translateY(-6px) rotate(-45deg); }
.theme-btn svg { width: 19px; height: 19px; fill: none; stroke: currentColor; stroke-width: 1.8; stroke-linecap: round; grid-area: 1 / 1; transition: transform 0.6s var(--spring), opacity 0.3s; }
.theme-btn .moon { fill: currentColor; stroke: none; }
[data-theme="dark"] .theme-btn .sun { opacity: 0; transform: rotate(-90deg) scale(0.4); }
[data-theme="light"] .theme-btn .moon { opacity: 0; transform: rotate(90deg) scale(0.4); }

/* ================= Sidebar ================= */
.sidebar {
  position: fixed; top: var(--topbar); bottom: 0; left: 0; width: var(--sidebar);
  overflow-y: auto; overscroll-behavior: contain;
  padding: 18px 14px calc(30px + var(--safe-b));
  border-right: 1px solid var(--line);
  background: color-mix(in srgb, var(--bg-2) 92%, transparent);
  z-index: 35;
  transition: transform 0.4s var(--ease);
}
.progress-box { margin: 0 4px 14px; }
.progress-label { display: flex; justify-content: space-between; font-size: 0.78rem; color: var(--muted); font-weight: 650; }
.progress-track { height: 7px; background: var(--panel-2); border-radius: 99px; overflow: hidden; margin-top: 6px; border: 1px solid var(--line); }
.progress-fill {
  height: 100%; width: 0; border-radius: 99px;
  background: linear-gradient(90deg, var(--accent), var(--violet), var(--accent-2));
  background-size: 200% 100%;
  animation: shimmer 4s linear infinite;
  transition: width 0.9s var(--ease);
}
.search-box { position: relative; margin-bottom: 10px; }
.search-box kbd { position: absolute; right: 10px; top: 50%; transform: translateY(-50%); pointer-events: none; }
#search {
  width: 100%; padding: 10px 36px 10px 12px; border-radius: 10px;
  border: 1px solid var(--line); background: var(--panel); color: var(--ink);
  font: inherit; font-size: 0.92rem; outline: none;
  transition: border-color 0.2s, box-shadow 0.2s;
}
#search:focus { border-color: var(--accent-2); box-shadow: 0 0 0 4px color-mix(in srgb, var(--accent-2) 20%, transparent); }
.nav-part { font-size: 0.68rem; text-transform: uppercase; letter-spacing: 0.09em; font-weight: 800; color: var(--faint); margin: 18px 8px 5px; }
#nav a {
  display: flex; align-items: center; gap: 9px; padding: 7px 9px; border-radius: 9px;
  color: var(--muted); font-size: 0.9rem; line-height: 1.35; position: relative;
  transition: background 0.2s, color 0.2s, transform 0.25s var(--ease);
}
#nav a.sub { margin-left: 16px; font-size: 0.84rem; }
#nav a:hover { background: var(--panel); color: var(--ink); text-decoration: none; transform: translateX(3px); }
#nav a.active { background: var(--panel); color: var(--ink); font-weight: 650; box-shadow: inset 0 0 0 1px var(--line); }
#nav a.active::before {
  content: ""; position: absolute; left: -14px; top: 7px; bottom: 7px; width: 3px; border-radius: 3px;
  background: linear-gradient(var(--accent), var(--violet)); animation: grow 0.4s var(--ease);
}
#nav .check {
  width: 18px; height: 18px; flex: none; display: grid; place-items: center; font-size: 0.66rem;
  border-radius: 50%; border: 1.5px solid var(--line-2); color: transparent;
  transition: all 0.4s var(--spring);
}
#nav a.done .check { background: var(--green); border-color: var(--green); color: #fff; transform: scale(1.08); }
.nav-title { flex: 1; min-width: 0; }
.legend { margin: 22px 8px 0; font-size: 0.78rem; color: var(--faint); display: grid; gap: 6px; }
.backdrop { position: fixed; inset: 0; background: rgba(5, 8, 14, 0.55); backdrop-filter: blur(2px); opacity: 0; pointer-events: none; transition: opacity 0.35s; z-index: 34; }

.tag { font-size: 0.62rem; font-weight: 800; text-transform: uppercase; letter-spacing: 0.06em; padding: 2px 6px; border-radius: 5px; flex: none; }
.tag.gap { background: color-mix(in srgb, var(--red) 16%, transparent); color: var(--red); }
.tag.core { background: color-mix(in srgb, var(--accent-2) 16%, transparent); color: var(--accent-2); }
.tag.refresh { background: color-mix(in srgb, var(--green) 16%, transparent); color: var(--green); }

/* ================= Main & TOC ================= */
.main { margin-left: var(--sidebar); margin-right: var(--toc); padding: calc(var(--topbar) + 34px) 48px 90px; min-height: 100vh; min-width: 0; }
.content, .pager { max-width: 880px; margin: 0 auto; }
.content { outline: none; min-width: 0; }
.toc { position: fixed; top: var(--topbar); right: 0; width: var(--toc); bottom: 0; overflow-y: auto; padding: 36px 18px; font-size: 0.82rem; }
.toc-title { font-weight: 800; text-transform: uppercase; letter-spacing: 0.09em; font-size: 0.68rem; color: var(--faint); margin-bottom: 10px; }
.toc a { display: block; color: var(--muted); padding: 4px 10px; border-left: 2px solid var(--line); line-height: 1.4; transition: color 0.2s, border-color 0.2s, background 0.2s; }
.toc a.h3 { padding-left: 22px; font-size: 0.78rem; }
.toc a:hover { color: var(--ink); text-decoration: none; background: color-mix(in srgb, var(--panel) 60%, transparent); }
.toc a.active { color: var(--accent); border-left-color: var(--accent); }
#mini-toc { display: none; }

/* loader */
.loader { position: fixed; top: var(--topbar); left: var(--sidebar); right: 0; height: 3px; opacity: 0; transition: opacity 0.2s; z-index: 30; display: flex; }
.loader.on { opacity: 1; }
.loader span { flex: 1; background: var(--accent); animation: load 1s ease-in-out infinite; }
.loader span:nth-child(2) { background: var(--violet); animation-delay: 0.15s; }
.loader span:nth-child(3) { background: var(--accent-2); animation-delay: 0.3s; }

/* ================= Content typography ================= */
.content h1 {
  font-size: clamp(1.75rem, 1.2rem + 2.4vw, 2.6rem); line-height: 1.12; letter-spacing: -0.03em; margin: 8px 0 14px;
  /* 200%-wide gradient: the sweep ends on "ink → orange → violet" across the title */
  background: linear-gradient(100deg, var(--ink) 0%, var(--ink) 24%, var(--accent) 40%, var(--violet) 50%, var(--violet) 100%);
  background-size: 200% 100%; -webkit-background-clip: text; background-clip: text; color: transparent;
  animation: titleSweep 1.6s var(--ease) both;
}
.content h2 {
  font-size: clamp(1.3rem, 1.1rem + 0.9vw, 1.6rem); letter-spacing: -0.02em;
  margin: 2.4em 0 0.7em; padding-bottom: 0.35em; border-bottom: 1px solid var(--line); position: relative;
}
.content h2::after {
  content: ""; position: absolute; left: 0; bottom: -1px; width: 56px; height: 2px; border-radius: 2px;
  background: linear-gradient(90deg, var(--accent), var(--violet));
}
.content h3 { font-size: 1.15rem; margin: 1.8em 0 0.45em; }
.content h4 { margin: 1.2em 0 0.35em; }
.content h2, .content h3 { scroll-margin-top: calc(var(--topbar) + 16px); }
.content p, .content li { overflow-wrap: break-word; }
.content li { margin: 0.28em 0; }
.content ul, .content ol { padding-left: 1.4em; }
.content hr { border: 0; border-top: 1px solid var(--line); margin: 2.5em 0; }
.anchor {
  font: 700 0.8em var(--mono); color: var(--faint); background: none; border: 0; cursor: pointer;
  margin-left: 8px; padding: 0 4px; opacity: 0; transition: opacity 0.2s, color 0.2s; vertical-align: middle;
}
h2:hover .anchor, h3:hover .anchor, .anchor:focus-visible { opacity: 1; }
.anchor:hover { color: var(--accent); }

.hero { position: relative; padding: 8px 0 22px; border-bottom: 1px solid var(--line); margin-bottom: 10px; isolation: isolate; }
.hero::before {
  content: ""; position: absolute; z-index: -1; width: 340px; height: 340px; right: -60px; top: -120px; border-radius: 50%;
  background: radial-gradient(circle, color-mix(in srgb, var(--accent) 22%, transparent), transparent 65%);
  filter: blur(10px); animation: float 9s ease-in-out infinite;
}
.kicker { display: inline-flex; align-items: center; gap: 8px; color: var(--accent); font-weight: 800; text-transform: uppercase; letter-spacing: 0.1em; font-size: 0.76rem; }
.kicker::before { content: ""; width: 18px; height: 2px; border-radius: 2px; background: currentColor; }
.lead { font-size: clamp(1rem, 0.95rem + 0.3vw, 1.13rem); color: var(--muted); margin: 0; }
.chips { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 16px; }
.chip {
  font-size: 0.78rem; padding: 4px 11px; border-radius: 99px; border: 1px solid var(--line);
  background: color-mix(in srgb, var(--panel) 80%, transparent); color: var(--muted); font-weight: 650;
  animation: fadeUp 0.6s var(--ease) both;
}
.chip:nth-child(2) { animation-delay: 0.06s; } .chip:nth-child(3) { animation-delay: 0.12s; } .chip:nth-child(4) { animation-delay: 0.18s; }

/* ================= Components ================= */
/* tables */
.table-wrap {
  margin: 1.2em 0; overflow-x: auto; border-radius: var(--radius); background: var(--panel);
  box-shadow: 0 0 0 1px var(--line); -webkit-overflow-scrolling: touch;
}
.content table { width: 100%; border-collapse: collapse; font-size: 0.92rem; }
.content th, .content td { padding: 10px 14px; text-align: left; vertical-align: top; border-bottom: 1px solid var(--line); }
.content th { background: var(--panel-2); font-size: 0.74rem; text-transform: uppercase; letter-spacing: 0.06em; color: var(--muted); white-space: nowrap; }
.content tr:last-child td { border-bottom: 0; }
.content tbody tr { transition: background 0.2s; }
.content tbody tr:hover { background: color-mix(in srgb, var(--accent-2) 5%, var(--panel)); }

.scroll-hint { display: none; margin: 1.2em 0 -0.9em; font-size: 0.74rem; font-weight: 700; color: var(--faint); text-align: right; letter-spacing: 0.04em; }
.scroll-hint.show { display: block; animation: nudge 2.4s ease-in-out 3; }
@keyframes nudge { 0%, 100% { transform: none; } 50% { transform: translateX(-6px); } }

/* callouts */
.callout {
  position: relative; border: 1px solid var(--line); border-left: 4px solid var(--accent-2);
  background: var(--panel); border-radius: 12px; padding: 13px 18px; margin: 1.3em 0;
}
.callout > :first-child { margin-top: 0; }
.callout > :last-child { margin-bottom: 0; }
.callout::before { display: block; font-weight: 800; font-size: 0.72rem; text-transform: uppercase; letter-spacing: 0.09em; margin-bottom: 5px; }
.callout.info::before { content: "ℹ Note"; color: var(--accent-2); }
.callout.tip { border-left-color: var(--green); }
.callout.tip::before { content: "✔ Tip"; color: var(--green); }
.callout.warn { border-left-color: var(--yellow); }
.callout.warn::before { content: "⚠ Pitfall"; color: var(--yellow); }
.callout.you { border-left-color: var(--violet); background: color-mix(in srgb, var(--violet) 6%, var(--panel)); }
.callout.you::before { content: "◆ From what you already know"; color: var(--violet); }
.callout.interview { border-left-color: var(--accent); background: color-mix(in srgb, var(--accent) 7%, var(--panel)); }
.callout.interview::before { content: "🎤 Interview angle"; color: var(--accent); }
#file-warning { margin-top: 0; }
#file-warning::before { content: "⚠ Setup"; }
pre.plain { background: var(--code-bg); color: #e6ebf2; padding: 10px 14px; border-radius: 8px; overflow-x: auto; font-size: 0.85rem; }

/* code */
figure.code {
  margin: 1.3em 0; border-radius: var(--radius); overflow: hidden; background: var(--code-bg);
  border: 1px solid #1f2a3a; box-shadow: var(--shadow); min-width: 0;
  transition: box-shadow 0.3s, border-color 0.3s;
}
figure.code:hover { border-color: #2c3b53; box-shadow: var(--shadow), var(--glow); }
figure.code figcaption {
  display: flex; align-items: center; gap: 10px; padding: 8px 12px; background: var(--code-head);
  border-bottom: 1px solid #1f2a3a; font: 600 0.72rem var(--mono); color: #8b98aa; min-width: 0;
}
.dots { display: inline-flex; gap: 5px; flex: none; }
.dots i { width: 9px; height: 9px; border-radius: 50%; background: #ff5f57; }
.dots i:nth-child(2) { background: #febc2e; }
.dots i:nth-child(3) { background: #28c840; }
figure.code .lang { text-transform: uppercase; color: #f59e4b; letter-spacing: 0.07em; flex: none; }
figure.code .file { color: #c9d4e3; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; min-width: 0; }
figure.code .copy {
  margin-left: auto; flex: none; font: inherit; color: #c9d4e3; background: #1c2738; border: 1px solid #2a3a52;
  border-radius: 7px; padding: 3px 11px; cursor: pointer; transition: background 0.2s, transform 0.15s, color 0.2s;
}
figure.code .copy:hover { background: #26354d; }
figure.code .copy:active { transform: scale(0.92); }
figure.code .copy.ok { color: #3fcf6b; border-color: #2f6b45; }
figure.code pre { margin: 0; padding: 15px 17px; overflow-x: auto; font-size: 0.84rem; line-height: 1.62; color: #d6deeb; tab-size: 4; outline: none; }
.c-com { color: #6d7d94; font-style: italic; }
.c-str { color: #a5e3a8; }
.c-kw { color: #ff9e64; font-weight: 600; }
.c-type { color: #7dcfff; }
.c-fn { color: #e8c872; }
.c-ann { color: #c792ea; }
.c-num { color: #f78c6c; }
.c-tag { color: #7dcfff; }
.c-attr { color: #e8c872; }
.c-key { color: #82aaff; }

/* exercises */
.exercise {
  position: relative; border: 1px dashed color-mix(in srgb, var(--green) 55%, var(--line));
  background: color-mix(in srgb, var(--green) 5%, var(--panel)); border-radius: var(--radius); padding: 15px 19px; margin: 1.7em 0;
}
.exercise > h4:first-child { margin-top: 0; color: var(--green); }
.exercise > h4:first-child::before { content: "✎ Exercise · "; }
.exercise figure.code { box-shadow: none; }
details { border: 1px solid var(--line); background: var(--panel); border-radius: 11px; margin: 0.8em 0; overflow: hidden; }
details > summary {
  cursor: pointer; padding: 10px 14px; font-weight: 650; list-style: none; user-select: none;
  transition: background 0.2s; display: flex; align-items: center; gap: 8px;
}
details > summary::-webkit-details-marker { display: none; }
details > summary::before { content: "▸"; display: inline-block; transition: transform 0.3s var(--spring); color: var(--accent); }
details[open] > summary::before { transform: rotate(90deg); }
details > summary:hover { background: var(--panel-2); }
details > :not(summary) { margin-left: 14px; margin-right: 14px; }
details[open] > :not(summary) { animation: fadeUp 0.4s var(--ease); }
details > :last-child:not(summary) { margin-bottom: 12px; }

/* quiz */
.quiz { border: 1px solid var(--line); background: var(--panel); border-radius: var(--radius); padding: 15px 19px; margin: 1.7em 0; transition: border-color 0.3s; }
.quiz.ok { border-color: color-mix(in srgb, var(--green) 55%, var(--line)); }
.quiz.bad { border-color: color-mix(in srgb, var(--red) 45%, var(--line)); }
.quiz > p:first-child { margin-top: 0; font-weight: 650; }
.quiz > p:first-child::before { content: "? Quick check · "; color: var(--accent-2); font-weight: 800; }
.quiz button[data-k] {
  display: flex; align-items: center; gap: 10px; width: 100%; text-align: left; font: inherit; font-size: 0.93rem; color: var(--ink);
  background: var(--panel-2); border: 1px solid var(--line); border-radius: 10px; padding: 9px 13px; margin: 7px 0; cursor: pointer;
  transition: border-color 0.2s, transform 0.25s var(--ease), background 0.2s;
}
.quiz button[data-k]::before {
  content: attr(data-k); flex: none; width: 24px; height: 24px; display: grid; place-items: center; border-radius: 7px;
  font: 800 0.72rem var(--mono); text-transform: uppercase; background: var(--panel); border: 1px solid var(--line); color: var(--muted);
}
.quiz:not(.answered) button[data-k]:hover { border-color: var(--accent-2); transform: translateX(4px); }
.quiz button.right { border-color: var(--green); background: color-mix(in srgb, var(--green) 13%, var(--panel)); animation: pop 0.45s var(--spring); }
.quiz button.right::before { content: "✓"; background: var(--green); color: #fff; border-color: var(--green); }
.quiz button.wrong { border-color: var(--red); background: color-mix(in srgb, var(--red) 11%, var(--panel)); animation: shake 0.4s; }
.quiz button.wrong::before { content: "✕"; background: var(--red); color: #fff; border-color: var(--red); }
.quiz.answered button[data-k]:not(.right):not(.wrong) { opacity: 0.55; }
.quiz .explain { display: none; margin-top: 10px; color: var(--muted); font-size: 0.93rem; padding: 10px 12px; border-radius: 9px; background: var(--panel-2); }
.quiz.answered .explain { display: block; animation: fadeUp 0.45s var(--ease); }

/* tiles */
.grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(min(240px, 100%), 1fr)); gap: 14px; margin: 1.2em 0; }
.grid > .tile {
  border: 1px solid var(--line); background: var(--panel); border-radius: var(--radius); padding: 15px 17px;
  transition: transform 0.35s var(--spring), border-color 0.25s, box-shadow 0.3s;
}
.grid > a.tile { color: var(--ink); display: block; }
.grid > .tile:hover { transform: translateY(-4px); border-color: var(--accent); box-shadow: var(--shadow), var(--glow); text-decoration: none; }
.tile h4 { margin: 0 0 4px; }
.tile p { margin: 0; color: var(--muted); font-size: 0.9rem; }

/* home: chapter grid + resume */
.resume {
  display: flex; flex-direction: column; gap: 2px; padding: 16px 20px; margin: 0 0 18px; border-radius: var(--radius);
  color: #fff; text-decoration: none !important;
  background: linear-gradient(120deg, var(--accent), var(--violet) 60%, var(--accent-2));
  background-size: 200% 200%; animation: gradientMove 8s ease infinite;
  box-shadow: 0 14px 34px color-mix(in srgb, var(--accent) 30%, transparent);
  transition: transform 0.35s var(--spring);
}
.resume:hover { transform: translateY(-3px) scale(1.01); }
.resume span { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.08em; opacity: 0.9; font-weight: 700; }
.resume strong { font-size: 1.12rem; }
.chapter-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(min(260px, 100%), 1fr)); gap: 12px; }
.chapter {
  display: flex; gap: 12px; align-items: flex-start; padding: 13px 15px; border-radius: 12px;
  border: 1px solid var(--line); background: var(--panel); color: var(--ink); position: relative; overflow: hidden;
  animation: fadeUp 0.55s var(--ease) both; animation-delay: calc(var(--i) * 35ms);
  transition: transform 0.35s var(--spring), border-color 0.25s, box-shadow 0.3s;
}
.chapter::after {
  content: ""; position: absolute; inset: 0; background: linear-gradient(120deg, transparent 30%, color-mix(in srgb, var(--accent) 10%, transparent), transparent 70%);
  transform: translateX(-100%); transition: transform 0.7s var(--ease);
}
.chapter:hover { transform: translateY(-3px); border-color: var(--accent); box-shadow: var(--shadow); text-decoration: none; }
.chapter:hover::after { transform: translateX(100%); }
.chapter.is-done { border-color: color-mix(in srgb, var(--green) 45%, var(--line)); }
.chapter-num { font: 800 1.15rem var(--mono); color: var(--faint); line-height: 1.4; }
.chapter.is-done .chapter-num { color: var(--green); }
.chapter-body { display: flex; flex-direction: column; gap: 3px; min-width: 0; }
.chapter-body strong { font-size: 0.95rem; line-height: 1.35; }
.chapter-part { font-size: 0.68rem; text-transform: uppercase; letter-spacing: 0.08em; color: var(--faint); font-weight: 700; }
.chapter-meta { display: flex; flex-wrap: wrap; align-items: center; gap: 8px; font-size: 0.76rem; color: var(--muted); }
.chapter-done { color: var(--green); font-weight: 700; }

/* reading list */
.reading { border: 1px solid var(--line); border-radius: var(--radius); padding: 10px 18px; background: var(--panel); margin: 1.5em 0; }
.reading::before { content: "📚 Read more"; display: block; font-weight: 800; font-size: 0.72rem; text-transform: uppercase; letter-spacing: 0.09em; color: var(--faint); margin-top: 4px; }
.reading ul { margin: 6px 0; padding-left: 20px; }
.reading li { font-size: 0.93rem; }

/* checklists */
.check-count { display: flex; align-items: center; gap: 12px; font-size: 0.82rem; color: var(--muted); font-weight: 650; margin-top: 8px; }
.check-count .progress-track { flex: 1; max-width: 260px; margin: 0; }
.checklist { list-style: none; padding: 0 !important; margin: 10px 0; display: grid; gap: 8px; }
.checklist li { margin: 0; }
.checklist label {
  display: flex; gap: 12px; align-items: flex-start; padding: 10px 14px; border-radius: 11px; cursor: pointer;
  border: 1px solid var(--line); background: var(--panel); transition: border-color 0.2s, background 0.3s, transform 0.25s var(--ease);
}
.checklist label:hover { border-color: var(--accent-2); transform: translateX(3px); }
.checklist input {
  appearance: none; -webkit-appearance: none; flex: none; width: 20px; height: 20px; margin: 3px 0 0; border-radius: 6px;
  border: 2px solid var(--line-2); background: var(--panel-2); display: grid; place-items: center; cursor: pointer;
  transition: all 0.3s var(--spring);
}
.checklist input::after { content: "✓"; color: #fff; font-size: 0.78rem; font-weight: 900; transform: scale(0); transition: transform 0.3s var(--spring); }
.checklist input:checked { background: var(--green); border-color: var(--green); }
.checklist input:checked::after { transform: scale(1); }
.checklist li.checked label { background: color-mix(in srgb, var(--green) 7%, var(--panel)); border-color: color-mix(in srgb, var(--green) 40%, var(--line)); color: var(--muted); }

/* inline deep-dive slot (htmx) */
.deep-btn {
  font: inherit; font-weight: 700; color: var(--accent); cursor: pointer; padding: 9px 15px; border-radius: 10px;
  background: color-mix(in srgb, var(--accent) 9%, var(--panel)); border: 1px solid color-mix(in srgb, var(--accent) 40%, var(--line));
  transition: transform 0.3s var(--spring), box-shadow 0.3s;
}
.deep-btn:hover { transform: translateY(-2px); box-shadow: var(--glow); }
.deep-btn.htmx-request { opacity: 0.6; cursor: progress; }
.inline-slot:not(:empty) { border-left: 3px solid var(--accent); padding-left: 18px; margin-top: 14px; animation: fadeUp 0.6s var(--ease); }

/* flashcards */
.deck-actions { display: flex; flex-wrap: wrap; gap: 10px; margin: 10px 0 14px; }
.deck-actions button {
  font: inherit; font-size: 0.86rem; font-weight: 650; cursor: pointer; color: var(--ink); background: var(--panel);
  border: 1px solid var(--line); border-radius: 9px; padding: 7px 14px; transition: border-color 0.2s, transform 0.25s var(--spring);
}
.deck-actions button:hover { border-color: var(--accent-2); transform: translateY(-2px); }
.cards { display: grid; grid-template-columns: repeat(auto-fill, minmax(min(270px, 100%), 1fr)); gap: 14px; }
.card { perspective: 1100px; cursor: pointer; min-height: 270px; outline: none; border-radius: var(--radius); }
.card:focus-visible { box-shadow: 0 0 0 2px var(--accent-2); }
.card.shuffled { animation: dealIn 0.5s var(--spring) both; }
.card-inner { position: relative; width: 100%; height: 100%; min-height: 270px; transition: transform 0.7s var(--spring); transform-style: preserve-3d; }
.card.flipped .card-inner { transform: rotateY(180deg); }
.card .q, .card .a {
  position: absolute; inset: 0; backface-visibility: hidden; -webkit-backface-visibility: hidden;
  border-radius: var(--radius); padding: 18px; border: 1px solid var(--line); overflow: auto; font-size: 0.9rem;
}
.card .q {
  background: radial-gradient(400px 200px at 100% 0%, color-mix(in srgb, var(--accent) 10%, transparent), transparent 70%), var(--panel);
  font-weight: 650; display: flex; flex-direction: column; justify-content: center; gap: 4px; transition: border-color 0.25s, box-shadow 0.3s;
}
.card .q::after { content: "tap to flip ↻"; position: absolute; right: 14px; bottom: 10px; font-size: 0.7rem; color: var(--faint); font-weight: 600; }
.card .q small { color: var(--accent); text-transform: uppercase; font-size: 0.66rem; letter-spacing: 0.09em; font-weight: 800; }
.card .a { background: var(--panel-2); transform: rotateY(180deg); color: var(--muted); line-height: 1.6; border-color: color-mix(in srgb, var(--accent-2) 35%, var(--line)); }
.card .a ul { padding-left: 18px; margin: 4px 0; }
.card:hover .q { border-color: var(--accent-2); box-shadow: var(--shadow); }

/* timeline */
.timeline { list-style: none; padding: 0 !important; margin: 1.3em 0; position: relative; counter-reset: step; }
.timeline::before { content: ""; position: absolute; left: 14px; top: 8px; bottom: 8px; width: 2px; background: linear-gradient(var(--accent), var(--violet), var(--accent-2)); opacity: 0.45; border-radius: 2px; }
.timeline li { position: relative; padding-left: 46px; margin: 0 0 14px; counter-increment: step; }
.timeline li::before {
  content: counter(step); position: absolute; left: 0; top: 1px; width: 30px; height: 30px; border-radius: 50%;
  display: grid; place-items: center; font-size: 0.78rem; font-weight: 800;
  background: var(--panel); border: 2px solid var(--accent); color: var(--accent); box-shadow: 0 0 0 4px var(--bg);
}

/* pager */
.pager { margin-top: 64px; padding-top: 26px; border-top: 1px solid var(--line); }
.pager:empty { display: none; }
.complete {
  font: inherit; font-weight: 700; cursor: pointer; display: block; margin: 0 auto 24px; padding: 11px 26px; border-radius: 99px;
  border: 1.5px solid var(--green); color: var(--green); background: transparent; transition: all 0.35s var(--spring);
}
.complete:hover { transform: scale(1.05); box-shadow: 0 8px 24px color-mix(in srgb, var(--green) 25%, transparent); }
.complete.is-done { background: var(--green); color: #fff; animation: pop 0.45s var(--spring); }
.pager-links { display: flex; justify-content: space-between; gap: 14px; }
.pager-links a {
  flex: 1; max-width: 48%; border: 1px solid var(--line); background: var(--panel); border-radius: var(--radius);
  padding: 13px 17px; color: var(--ink); font-weight: 650; transition: border-color 0.2s, transform 0.3s var(--spring), box-shadow 0.3s;
}
.pager-links a small { display: block; color: var(--faint); font-weight: 600; }
.pager-links a.next { text-align: right; margin-left: auto; }
.pager-links a:hover { border-color: var(--accent); text-decoration: none; transform: translateY(-3px); box-shadow: var(--shadow); }

/* floating bits */
.to-top {
  position: fixed; right: 22px; bottom: calc(22px + var(--safe-b)); width: 44px; height: 44px; border-radius: 50%; z-index: 30;
  border: 1px solid var(--line); background: var(--panel); color: var(--ink); font-size: 1.1rem; cursor: pointer; box-shadow: var(--shadow);
  opacity: 0; transform: translateY(16px) scale(0.8); pointer-events: none; transition: all 0.4s var(--spring);
}
.to-top.show { opacity: 1; transform: none; pointer-events: auto; }
.to-top:hover { border-color: var(--accent); color: var(--accent); }
.toast {
  position: fixed; left: 50%; bottom: calc(26px + var(--safe-b)); z-index: 60; transform: translate(-50%, 30px); opacity: 0; pointer-events: none;
  background: var(--ink); color: var(--bg); padding: 9px 18px; border-radius: 99px; font-size: 0.88rem; font-weight: 650;
  box-shadow: var(--shadow); transition: all 0.45s var(--spring); max-width: calc(100vw - 32px); text-align: center;
}
.toast.show { opacity: 1; transform: translate(-50%, 0); }
.spark { position: fixed; z-index: 70; width: 7px; height: 7px; border-radius: 2px; pointer-events: none; animation: spark 0.75s var(--ease) forwards; }

/* ================= Animations ================= */
.page-enter { animation: pageIn 0.6s var(--ease); }
.reveal { opacity: 0; transform: translateY(16px); transition: opacity 0.7s var(--ease), transform 0.7s var(--ease); }
.reveal.in { opacity: 1; transform: none; }
@keyframes pageIn { from { opacity: 0; transform: translateY(20px); filter: blur(4px); } to { opacity: 1; transform: none; filter: none; } }
@keyframes fadeUp { from { opacity: 0; transform: translateY(10px); } to { opacity: 1; transform: none; } }
@keyframes grow { from { transform: scaleY(0); } to { transform: scaleY(1); } }
@keyframes shake { 20%, 60% { transform: translateX(-6px); } 40%, 80% { transform: translateX(6px); } }
@keyframes pop { 50% { transform: scale(1.06); } }
@keyframes load { 0%, 100% { opacity: 0.25; } 50% { opacity: 1; } }
@keyframes shimmer { to { background-position: -200% 0; } }
@keyframes gradientMove { 0%, 100% { background-position: 0% 50%; } 50% { background-position: 100% 50%; } }
@keyframes titleSweep { from { background-position: 100% 0; } to { background-position: 0% 0; } }
@keyframes float { 0%, 100% { transform: translate(0, 0) scale(1); } 50% { transform: translate(-30px, 20px) scale(1.08); } }
@keyframes dealIn { from { opacity: 0; transform: translateY(18px) rotate(-3deg) scale(0.95); } to { opacity: 1; transform: none; } }
@keyframes spark { from { transform: translate(-50%, -50%) scale(1); opacity: 1; } to { transform: translate(calc(-50% + var(--dx)), calc(-50% + var(--dy))) scale(0.2) rotate(240deg); opacity: 0; } }
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation: none !important; transition: none !important; scroll-behavior: auto !important; }
  .reveal { opacity: 1; transform: none; }
  .content h1 { background-position: 0 0; }
}

/* ================= Responsive ================= */
@media (max-width: 1280px) {
  .toc { display: none; }
  .main { margin-right: 0; }
  #mini-toc { display: block; margin: 14px 0 6px; }
  #mini-toc summary small { margin-left: auto; color: var(--faint); font-weight: 600; font-size: 0.78rem; }
  #mini-toc nav { display: grid; padding: 4px 0 8px; max-height: 50vh; overflow-y: auto; }
  #mini-toc nav a { padding: 6px 10px; border-left: 2px solid var(--line); color: var(--muted); font-size: 0.88rem; line-height: 1.4; }
  #mini-toc nav a.h3 { padding-left: 24px; font-size: 0.82rem; }
  #mini-toc nav a.active { color: var(--accent); border-left-color: var(--accent); }
}
@media (max-width: 960px) {
  #menu-btn { display: grid; }
  .kbd-hint { display: none; }
  .sidebar { transform: translateX(-102%); width: min(86vw, 330px); box-shadow: var(--shadow); background: var(--bg-2); }
  body.nav-open .sidebar { transform: none; }
  body.nav-open .backdrop { opacity: 1; pointer-events: auto; }
  body.nav-open { overflow: hidden; }
  .main { margin-left: 0; padding: calc(var(--topbar) + 22px) 28px 80px; }
  .loader { left: 0; }
}
@media (max-width: 640px) {
  :root { --topbar: 56px; }
  body { font-size: 15.5px; line-height: 1.65; }
  .topbar { padding: 0 12px; gap: 10px; }
  .brand small { display: none; }
  .main { padding: calc(var(--topbar) + 16px) 16px 72px; }
  .content h2 { margin-top: 2em; }
  .hero::before { width: 220px; height: 220px; right: -80px; top: -90px; }
  .content th, .content td { padding: 8px 11px; font-size: 0.86rem; }
  .content th { white-space: normal; }
  figure.code { margin-left: -4px; margin-right: -4px; border-radius: 11px; }
  figure.code pre { font-size: 0.78rem; padding: 12px 13px; }
  figure.code .dots { display: none; }
  .callout, .exercise, .quiz { padding: 12px 14px; }
  details > :not(summary) { margin-left: 10px; margin-right: 10px; }
  .timeline li { padding-left: 42px; }
  .pager-links { flex-direction: column; }
  .pager-links a { max-width: 100%; }
  .pager-links a.next { text-align: left; }
  .card, .card-inner { min-height: 300px; }
  .to-top { right: 14px; bottom: calc(14px + var(--safe-b)); }
}
@media (max-width: 380px) {
  .brand span:not(.brand-cup) { display: none; }
}
@media (hover: none) {
  .anchor { display: none; }
}

/* ================= Print ================= */
@media print {
  .topbar, .sidebar, .toc, .pager, .to-top, .toast, .read-progress, .loader, #mini-toc, .anchor, .deck-actions, figure.code .copy { display: none !important; }
  body { background: #fff; color: #000; }
  .main { margin: 0; padding: 0; }
  .reveal { opacity: 1 !important; transform: none !important; }
  .content h1 { color: #000; background: none; }
  .quiz .explain, details > * { display: block !important; }
  .card .a { position: static; transform: none; }
  .card .q { position: static; }
  .card-inner { transform: none !important; min-height: 0; }
}