/*  Organic Chemistry from the Beginning — design system
    ------------------------------------------------------
    The Curionode monograph look — warm paper, Fraunces display, Source Serif
    body, JetBrains Mono for formulas and readouts. Molecules are drawn on
    canvas in the figure palette; the sketch pad, the arrow bench and the
    challenges add their own small controls below.

    Colours are tokens. The dark values appear twice, once for a reader whose
    system asks for dark (no script, so no flash of light page) and once for an
    explicit choice; tools/build.py fails if the two copies drift.
*/
@import url('../vendor/fonts/fonts.css');

:root {
    --paper: #fbf8f3;  --paper-deep: #f4ede0;  --paper-vellum: #f0e9da;  --paper-rule: #e3dac6;
    --ink: #1c1c1f;  --ink-soft: #3a3a3f;  --ink-mute: #6e6e74;  --ink-faint: #9a958b;
    --red: #b8312f;  --red-tint: #f5e7e3;
    --blue: #1d4ed8;  --blue-tint: #e6ecf6;
    --teal: #0f6e6a;  --teal-tint: #e1eeec;
    --plum: #5a3a7a;  --plum-tint: #ece2f0;
    --sienna: #a8530c;  --sienna-tint: #f3e8d8;
    --olive: #5a5a1c;  --olive-tint: #ece6cc;
    --ochre: #b3791f;  --ochre-tint: #f4e6c8;
    --green: #2d6a4f;  --green-tint: #e0ede4;
    --input: #fffefb;
    --hl-1: rgba(29, 78, 216, 0.16);  --hl-2: rgba(179, 121, 31, 0.22);
    --fig-grid: #cfc6b0;  --fig-paper: #fffdf7;  --fig-cell: #fffefb;  --fig-rule: #e3dac6;
    --fig-ink: #1c1c1f;  --fig-muted: #6e6e74;  --fig-faint: #9a958b;
    --fig-blue: #1d4ed8;  --fig-red: #b8312f;  --fig-green: #2d6a4f;  --fig-teal: #0f6e6a;
    --fig-plum: #5a3a7a;  --fig-ochre: #b3791f;  --fig-sienna: #a8530c;  --fig-olive: #5a5a1c;
    --shadow: 0 2px 6px rgba(28, 28, 31, 0.06);
    --shadow-lg: 0 6px 20px rgba(28, 28, 31, 0.10);
    --font-display: 'Fraunces', 'Iowan Old Style', Georgia, serif;
    --font-body: 'Source Serif 4', 'Iowan Old Style', Georgia, serif;
    --font-mono: 'JetBrains Mono', ui-monospace, Menlo, Consolas, monospace;
    --font-zh: 'PingFang SC', 'Hiragino Sans GB', 'Noto Serif CJK SC', 'Source Han Serif SC', 'Songti SC', 'Microsoft YaHei', serif;
}

@media (prefers-color-scheme: dark) {
    :root:not([data-theme="light"]) {
    --paper: #17150f;  --paper-deep: #1e1b14;  --paper-vellum: #242017;  --paper-rule: #3a3427;
    --ink: #ece5d6;  --ink-soft: #c8c0ae;  --ink-mute: #9b9384;  --ink-faint: #756e60;
    --red: #e2706a;  --red-tint: #3b211f;
    --blue: #82a8f4;  --blue-tint: #1d2740;
    --teal: #4fb5ae;  --teal-tint: #16302e;
    --plum: #b492d8;  --plum-tint: #2c2339;
    --sienna: #e28c48;  --sienna-tint: #3b2617;
    --olive: #b7b662;  --olive-tint: #2f2e19;
    --ochre: #e2b257;  --ochre-tint: #3b3017;
    --green: #6cba8e;  --green-tint: #1a3026;
    --input: #1c1a13;
    --hl-1: rgba(130, 168, 244, 0.26);  --hl-2: rgba(226, 178, 87, 0.26);
    --fig-grid: #3a3427;  --fig-paper: #1a1710;  --fig-cell: #201d16;  --fig-rule: #3a3427;
    --fig-ink: #ece5d6;  --fig-muted: #9b9384;  --fig-faint: #756e60;
    --fig-blue: #82a8f4;  --fig-red: #e2706a;  --fig-green: #6cba8e;  --fig-teal: #4fb5ae;
    --fig-plum: #b492d8;  --fig-ochre: #e2b257;  --fig-sienna: #e28c48;  --fig-olive: #b7b662;
    --shadow: 0 2px 6px rgba(0, 0, 0, 0.38);
    --shadow-lg: 0 6px 20px rgba(0, 0, 0, 0.50);
    }
}
:root[data-theme="dark"] {
    --paper: #17150f;  --paper-deep: #1e1b14;  --paper-vellum: #242017;  --paper-rule: #3a3427;
    --ink: #ece5d6;  --ink-soft: #c8c0ae;  --ink-mute: #9b9384;  --ink-faint: #756e60;
    --red: #e2706a;  --red-tint: #3b211f;
    --blue: #82a8f4;  --blue-tint: #1d2740;
    --teal: #4fb5ae;  --teal-tint: #16302e;
    --plum: #b492d8;  --plum-tint: #2c2339;
    --sienna: #e28c48;  --sienna-tint: #3b2617;
    --olive: #b7b662;  --olive-tint: #2f2e19;
    --ochre: #e2b257;  --ochre-tint: #3b3017;
    --green: #6cba8e;  --green-tint: #1a3026;
    --input: #1c1a13;
    --hl-1: rgba(130, 168, 244, 0.26);  --hl-2: rgba(226, 178, 87, 0.26);
    --fig-grid: #3a3427;  --fig-paper: #1a1710;  --fig-cell: #201d16;  --fig-rule: #3a3427;
    --fig-ink: #ece5d6;  --fig-muted: #9b9384;  --fig-faint: #756e60;
    --fig-blue: #82a8f4;  --fig-red: #e2706a;  --fig-green: #6cba8e;  --fig-teal: #4fb5ae;
    --fig-plum: #b492d8;  --fig-ochre: #e2b257;  --fig-sienna: #e28c48;  --fig-olive: #b7b662;
    --shadow: 0 2px 6px rgba(0, 0, 0, 0.38);
    --shadow-lg: 0 6px 20px rgba(0, 0, 0, 0.50);
}

/* ─── Base ─────────────────────────────────────────────────── */

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
    margin: 0;
    background: var(--paper);
    color: var(--ink);
    font: 17px/1.62 var(--font-body);
    font-optical-sizing: auto;
    text-rendering: optimizeLegibility;
    /* No programming ligatures in formulas and readouts. */
    font-variant-ligatures: no-contextual;
}
code, pre, kbd, samp, input, textarea, .pat-input { font-variant-ligatures: none; }
::selection { background: var(--ochre-tint); }
a { color: var(--blue); text-decoration-thickness: 1px; text-underline-offset: 2px; }
code, kbd, .mono { font-family: var(--font-mono); font-size: 0.86em; }
p code, li code, dd code, td code, .prose code, .info-box code, .marginalia code, .key-concept code {
    background: var(--paper-deep);
    border: 1px solid var(--paper-rule);
    border-radius: 3px;
    padding: 0 0.28em;
    white-space: pre-wrap;
}
em { font-style: italic; }
button { font: inherit; color: inherit; }
.skip-link { position: absolute; left: -9999px; }
.skip-link:focus { left: 12px; top: 12px; z-index: 99; background: var(--paper); padding: 6px 10px; }
:focus-visible { outline: 2px solid var(--blue); outline-offset: 2px; }

/* ─── Topbar ───────────────────────────────────────────────── */

.topbar {
    position: sticky; top: 0; z-index: 20;
    display: flex; align-items: center; justify-content: space-between;
    padding: 14px 32px;
    background: color-mix(in srgb, var(--paper) 90%, transparent);
    backdrop-filter: blur(6px);
    border-bottom: 1px solid var(--paper-rule);
}
.topbar-left { display: flex; align-items: baseline; gap: 22px; min-width: 0; }
.topbar-back {
    font: 500 11px/1 var(--font-mono); letter-spacing: 0.12em; text-transform: uppercase;
    color: var(--ink-mute); text-decoration: none; white-space: nowrap;
}
.topbar-back:hover { color: var(--red); }
.topbar-title { font: 400 19px/1.2 var(--font-display); white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.topbar-title .icon {
    font: 600 12px/1 var(--font-mono); letter-spacing: 0.14em; text-transform: uppercase;
    color: var(--red); margin-right: 10px;
}
.lang-btn {
    border: 1px solid var(--paper-rule); background: var(--paper);
    font: 500 12px/1 var(--font-mono); padding: 6px 12px; border-radius: 3px; cursor: pointer;
}
.lang-btn:hover { border-color: var(--ink-mute); }

/* ─── The plate ────────────────────────────────────────────── */

.main-content { max-width: 920px; margin: 0 auto; padding: 36px 32px 80px; }
.plate-meta {
    display: flex; justify-content: space-between; gap: 16px; flex-wrap: wrap;
    padding-bottom: 10px; border-bottom: 1px solid var(--paper-rule);
    font: 500 11px/1.6 var(--font-mono); letter-spacing: 0.12em; text-transform: uppercase; color: var(--ink-mute);
}
.plate-meta b { color: var(--red); font-weight: 600; margin-right: 8px; }
.verb-chip {
    display: inline-block; margin-left: 6px; padding: 0 5px;
    border: 1px solid var(--blue); color: var(--blue); border-radius: 2px;
    font-size: 10px; letter-spacing: 0.08em;
}
h1.plate-title {
    font: 400 clamp(38px, 6vw, 58px)/1.04 var(--font-display);
    font-variation-settings: 'opsz' 144, 'SOFT' 30;
    letter-spacing: -0.02em;
    margin: 34px 0 14px;
}
h1.plate-title em { color: var(--red); }
.plate-deck { font: italic 20px/1.45 var(--font-body); color: var(--ink-soft); margin: 0 0 34px; max-width: 700px; }

.info-box.lede {
    border-left: 3px solid var(--ink); padding: 2px 0 2px 18px; margin: 0 0 30px; max-width: 700px;
}
.info-box.lede p { margin: 0 0 12px; }
.info-box.lede > p:first-child::first-letter,
.info-box.lede > :first-child::first-letter {
    float: left; font: 400 66px/0.84 var(--font-display); color: var(--red);
    margin: 6px 10px 0 0;
}
.info-box.lede > em {
    display: block; padding-top: 12px; margin-top: 4px; border-top: 1px solid var(--paper-rule);
    font-size: 15px; color: var(--ink-soft);
}

.formula-group {
    display: flex; flex-wrap: wrap; gap: 18px 40px; align-items: center;
    background: var(--paper-deep); border-top: 1px solid var(--paper-rule); border-bottom: 1px solid var(--paper-rule);
    padding: 22px 26px; margin: 0 0 30px; max-width: 700px;
}
.formula { position: relative; font-size: 17px; overflow-x: auto; }
.formula[data-eq]::after {
    content: '(' attr(data-eq) ')'; margin-left: 16px;
    font: italic 13px var(--font-body); color: var(--ink-faint);
}

.learning-objectives { border-top: 1px solid var(--ink); padding-top: 14px; margin: 0 0 34px; max-width: 700px; }
.learning-objectives-title, .section-title, .try-title, .flavours-title, .verb-trail-title {
    font: 600 11px/1.4 var(--font-mono); letter-spacing: 0.14em; text-transform: uppercase; color: var(--ink-mute);
}
.learning-objectives-title::before { content: '§ '; color: var(--red); }
.learning-objectives ul { list-style: none; padding: 0; margin: 12px 0 0; counter-reset: obj; }
.learning-objectives li { counter-increment: obj; position: relative; padding: 6px 0 6px 36px; border-bottom: 1px solid var(--paper-rule); }
.learning-objectives li::before {
    content: counter(obj, decimal-leading-zero); position: absolute; left: 0; top: 7px;
    font: italic 14px var(--font-display); color: var(--red);
}
.section-title { margin: 20px 0 16px; display: flex; align-items: center; gap: 12px; }
.section-title::before { content: ''; width: 26px; border-top: 1px solid var(--ink-mute); }

h2 { font: 400 30px/1.2 var(--font-display); letter-spacing: -0.01em; margin: 44px 0 14px; }
.prose { max-width: 700px; }
.prose p { margin: 0; }
.prose p + p { text-indent: 1.4em; margin-top: 12px; }
.marginalia {
    margin: 28px 0; padding: 12px 16px; max-width: 760px;
    border-left: 2px solid var(--red); background: var(--red-tint);
    font: italic 15px/1.55 var(--font-body); color: var(--ink-soft);
}
.flavours-box {
    margin: 26px 0; padding: 14px 18px; max-width: 760px;
    border: 1px solid var(--paper-rule); background: var(--paper-deep);
    font-size: 15px;
}
.flavours-box p { margin: 6px 0 0; }
dl.terms { max-width: 700px; margin: 0; }
dl.terms dt { font: italic 18px var(--font-display); margin-top: 14px; }
dl.terms dd { margin: 4px 0 0; padding-bottom: 12px; border-bottom: 1px solid var(--paper-rule); color: var(--ink-soft); }
.verb-trail { margin: 34px 0 0; max-width: 700px; font-size: 15px; }
.verb-trail ul { list-style: none; padding: 0; margin: 8px 0 0; }
.verb-trail li { padding: 4px 0; }
.verb-trail li b { font: 600 11px var(--font-mono); letter-spacing: 0.1em; text-transform: uppercase; color: var(--blue); margin-right: 10px; }
.key-concept {
    margin: 40px 0; padding: 4px 0 4px 22px; max-width: 700px;
    border-left: 3px solid var(--red);
    font: italic 21px/1.45 var(--font-body);
}
.key-concept::before {
    content: 'In short'; display: block; margin-bottom: 6px;
    font: 600 11px/1 var(--font-mono); font-style: normal; letter-spacing: 0.14em; text-transform: uppercase; color: var(--red);
}
html[lang="zh"] .key-concept::before, html[lang="zh-CN"] .key-concept::before { content: '要点'; }
.key-concept strong { font-weight: 600; }
.section-break { text-align: center; margin: 46px 0 20px; color: var(--ink-faint); }
.section-break::before { content: '⁂'; font-size: 22px; }
.nav-footer {
    display: flex; justify-content: space-between; gap: 12px; flex-wrap: wrap;
    border-top: 1px solid var(--paper-rule); padding-top: 16px;
    font: 500 12px var(--font-mono); letter-spacing: 0.08em; text-transform: uppercase;
}
.nav-footer a { color: var(--ink-soft); text-decoration: none; }
.nav-footer a:hover { color: var(--red); }
.nav-footer a.nav-report { color: var(--ink-faint); }
.xref { color: var(--blue); }
.course-map { display: grid; grid-template-columns: repeat(auto-fill, minmax(200px, 1fr)); gap: 10px; margin: 20px 0; }
.xref-card {
    display: block; padding: 12px 14px; border: 1px solid var(--paper-rule); text-decoration: none; color: var(--ink-soft);
    font-size: 14px; background: var(--paper);
}
.xref-card b { display: block; color: var(--ink); font: 400 17px/1.3 var(--font-display); margin-bottom: 4px; }
.xref-card span { display: block; margin-top: 6px; font: 11px var(--font-mono); color: var(--ink-faint); }

/* ─── Figures ──────────────────────────────────────────────── */

.figure { margin: 0 0 26px; counter-increment: fig; }
main { counter-reset: fig; }
.figure-canvas {
    position: relative; background: var(--fig-paper); border: 1px solid var(--paper-rule);
    box-shadow: var(--shadow);
}
.figure-canvas canvas { display: block; width: 100%; }
.figure-caption {
    margin-top: 10px; font: italic 14px/1.5 var(--font-body); color: var(--ink-soft); max-width: 760px;
}
.figure-caption::before {
    content: 'Fig. ' counter(fig) '.'; margin-right: 8px;
    font: 600 11px var(--font-mono); font-style: normal; letter-spacing: 0.1em; text-transform: uppercase; color: var(--red);
}
html[lang="zh"] .figure-caption::before { content: '图 ' counter(fig); }
.fig-controls {
    display: flex; flex-wrap: wrap; gap: 8px; align-items: center;
    padding: 10px 14px; border-top: 1px solid var(--paper-rule); background: var(--paper);
    font: 12px var(--font-mono);
}

/* ─── Buttons and small controls ───────────────────────────── */

.btn, .seg button, .tabs button {
    border: 1px solid var(--paper-rule); background: var(--paper); color: var(--ink-soft);
    font: 500 12px/1 var(--font-mono); padding: 7px 11px; border-radius: 3px; cursor: pointer;
}
.btn:hover, .seg button:hover, .tabs button:hover { border-color: var(--ink-mute); color: var(--ink); }
.btn.primary { background: var(--ink); color: var(--paper); border-color: var(--ink); }
.btn.warn { color: var(--red); border-color: var(--red); }
.seg { display: inline-flex; flex-wrap: wrap; gap: 0; }
.seg button { border-radius: 0; margin-left: -1px; }
.seg button:first-child { border-radius: 3px 0 0 3px; margin-left: 0; }
.seg button:last-child { border-radius: 0 3px 3px 0; }
.seg button[aria-pressed="true"], .tabs button[aria-selected="true"] { background: var(--ink); color: var(--paper); border-color: var(--ink); position: relative; }
input[type="range"] { accent-color: var(--red); }

/* ─── Molecule tools ───────────────────────────────────────── */

.tool-row { display: flex; flex-wrap: wrap; gap: 6px; align-items: center; padding: 8px 12px; border-top: 1px solid var(--paper-rule); background: var(--paper); font: 12px var(--font-mono); }
.tool-row .lab { font: 600 10px var(--font-mono); letter-spacing: 0.12em; text-transform: uppercase; color: var(--ink-faint); margin-right: 4px; }
.tool-row button[aria-pressed="true"] { background: var(--ink); color: var(--paper); border-color: var(--ink); }
.tool-row .sep { width: 1px; align-self: stretch; background: var(--paper-rule); margin: 0 4px; }
.fig-note { padding: 8px 14px; border-top: 1px solid var(--paper-rule); background: var(--paper); font: 14px/1.5 var(--font-body); color: var(--ink-soft); min-height: 1.5em; }
.fig-note b { font-weight: 600; color: var(--ink); }
.fig-note .warn { color: var(--red); }
.text-input { border: 1px solid var(--paper-rule); background: var(--input); color: var(--ink); font: 15px/1.4 var(--font-mono); padding: 5px 8px; border-radius: 3px; min-width: 0; }
.text-input:focus { outline: none; border-color: var(--blue); }
.text-input.bad { border-color: var(--red); }

/* ─── Challenges ───────────────────────────────────────────── */

.try-block { margin: 30px 0 10px; }
.challenge { border: 1px solid var(--paper-rule); background: var(--paper); margin: 12px 0; padding: 14px 16px; }
.challenge-head { display: flex; justify-content: space-between; align-items: baseline; gap: 12px; }
.challenge-q { font-size: 16px; }
.challenge-state { font: 600 11px var(--font-mono); letter-spacing: 0.1em; text-transform: uppercase; color: var(--ink-faint); white-space: nowrap; }
.challenge.solved { border-color: var(--green); background: var(--green-tint); }
.challenge.solved .challenge-state { color: var(--green); }
.challenge .work { margin-top: 10px; }
.challenge .work .figure-canvas { box-shadow: none; }
.challenge .answer-row { display: flex; gap: 8px; align-items: center; flex-wrap: wrap; margin-top: 10px; }
.challenge .answer-row .text-input { flex: 1 1 220px; }
.challenge .feedback { font: 13px/1.5 var(--font-mono); margin-top: 8px; min-height: 1.2em; white-space: pre-wrap; }
.challenge .feedback.ok { color: var(--green); }
.challenge .feedback.no { color: var(--red); }
.challenge .reveal { margin-top: 8px; font: 12px var(--font-mono); color: var(--ink-mute); }
.challenge .reveal summary { cursor: pointer; }
.opts { display: grid; grid-template-columns: repeat(auto-fill, minmax(180px, 1fr)); gap: 8px; margin-top: 10px; }
.opt { border: 1px solid var(--paper-rule); background: var(--fig-paper); cursor: pointer; padding: 6px; border-radius: 3px; text-align: center; font: 14px var(--font-body); color: var(--ink); }
.opt canvas { display: block; width: 100%; }
.opt:hover { border-color: var(--ink-mute); }
.opt.right { border-color: var(--green); background: var(--green-tint); }
.opt.wrong { border-color: var(--red); background: var(--red-tint); }
.opt .cap { display: block; font: 12px var(--font-mono); color: var(--ink-mute); margin-top: 4px; }
.opts.text { grid-template-columns: 1fr; }
.opts.text .opt { text-align: left; padding: 8px 12px; }
.tests-head { font: 600 10px var(--font-mono); letter-spacing: 0.12em; text-transform: uppercase; color: var(--ink-faint); margin-top: 10px; }

/* ─── Knowledge check ──────────────────────────────────────── */

.quiz-container { margin: 46px 0 0; max-width: 760px; }
.quiz-title { font: 400 28px var(--font-display); margin: 0 0 4px; }
.quiz-sub { font: italic 15px var(--font-body); color: var(--ink-mute); margin: 0 0 16px; }
.quiz-q { border-top: 1px solid var(--paper-rule); padding: 16px 0; }
.quiz-q-text { margin: 0 0 10px; }
.quiz-q-text b { font: 600 12px var(--font-mono); color: var(--red); margin-right: 8px; }
.quiz-opts { display: grid; gap: 6px; }
.quiz-opt {
    text-align: left; border: 1px solid var(--paper-rule); background: var(--paper); cursor: pointer;
    padding: 8px 12px; border-radius: 3px; font: 15px/1.45 var(--font-body);
}
.quiz-opt:hover:not([disabled]) { border-color: var(--ink-mute); }
.quiz-opt.right { border-color: var(--green); background: var(--green-tint); }
.quiz-opt.wrong { border-color: var(--red); background: var(--red-tint); }
.quiz-opt[disabled] { cursor: default; }
.quiz-expl { margin: 10px 0 0; font-size: 15px; color: var(--ink-soft); padding-left: 12px; border-left: 2px solid var(--paper-rule); }
.quiz-score { font: 600 13px var(--font-mono); margin-top: 14px; color: var(--ink-soft); }

/* ─── Chinese ──────────────────────────────────────────────── */

html[lang="zh"] body { font-family: var(--font-body), var(--font-zh); }
html[lang="zh"] h1.plate-title, html[lang="zh"] h2 { font-family: var(--font-display), var(--font-zh); letter-spacing: 0; }
html[lang="zh"] .info-box.lede > :first-child::first-letter { float: none; font: inherit; color: inherit; margin: 0; }
html[lang="zh"] .plate-meta, html[lang="zh"] .section-title { letter-spacing: 0.04em; }
html[lang="zh"] .prose p + p { text-indent: 2em; }

/* ─── Narrow viewports ─────────────────────────────────────── */

@media (max-width: 640px) {
    body { font-size: 16px; }
    .topbar { padding: 12px 16px; }
    .topbar-title .icon { display: none; }
    .main-content { padding: 24px 16px 60px; }
    .bench-row { padding: 8px 10px; }
    .bench-label { min-width: 0; }
    .tests { grid-template-columns: 1fr; }
}

.rail-stats > span { margin-right: 18px; }
.rail-stats .stat-label { font: 600 10px/1 var(--font-mono); letter-spacing: 0.04em; color: var(--ink-faint); }
.formula-text sub { font-size: 0.72em; }

/* drill rounds */
.drill-score { padding: 10px 14px 4px; font: 600 11px/1.4 var(--font-mono); color: var(--ink-faint); letter-spacing: 0.04em; }
.drill-q { padding: 6px 14px 8px; }
[id="fig"] > .opts, [id="rounds"] > .opts { padding: 0 14px; }
[id="fig"] > .feedback, [id="rounds"] > .feedback { padding: 4px 14px; }
[id="fig"] > .tool-row, [id="rounds"] > .tool-row { padding: 8px 14px 12px; }
.btn[disabled], .btn[disabled]:hover { opacity: 0.4; cursor: default; }