/* Visual layer shared by the existing server-rendered pages. Business selectors and forms stay in place. */
:root {
    color-scheme: dark;
    --ink: #e5e5e7;
    --muted: #a4a7af;
    --green: #b9cbbd;
    --line: #33363b;
    --paper: #222428;
    --bg: #18191b;
    --accent: #2a332e;
    --side: #141517;
    --field: #18191b;
    --primary: #e5e5e7;
    --primary-text: #18191b;
    --error: #ffb4a8;
    --notice: #24362d;
    --warning: #ffe0a6;
    --warning-bg: #453821;
    --reading-font-size: 18px;
    font-family: "Segoe UI Variable", "Segoe UI", "Microsoft YaHei UI", sans-serif;
    font-size: 15px;
}
:root[data-reading-theme="light"] {
    color-scheme: light;
    --ink: #242628; --muted: #62666a; --green: #315d46; --line: #c9ccc6;
    --paper: #f2f3f0; --bg: #fafaf8; --accent: #e5eae3; --side: #efefec;
    --field: #fafaf8; --primary: #242628; --primary-text: #fafaf8;
    --error: #9b3029; --notice: #e5eee3; --warning: #714b13; --warning-bg: #fff0d3;
}
:root[data-reading-theme="sepia"] {
    color-scheme: light;
    --ink: #453b2d; --muted: #6d5f4a; --green: #3e6244; --line: #c8bda4;
    --paper: #faf3df; --bg: #f3ecd9; --accent: #e6dfc8; --side: #ebe3ce;
    --field: #f3ecd9; --primary: #453b2d; --primary-text: #faf3df;
    --error: #9b3029; --notice: #e1e5ce; --warning: #714b13; --warning-bg: #f6e6bf;
}
:root[data-reading-theme="contrast"] {
    color-scheme: dark;
    --ink: #fff; --muted: #ddd; --green: #b9ffcc; --line: #aaa;
    --paper: #080808; --bg: #000; --accent: #163621; --side: #000;
    --field: #000; --primary: #fff; --primary-text: #000;
    --error: #ffb4a8; --notice: #123720; --warning: #ffe0a6; --warning-bg: #453821;
}
body { color: var(--ink); background: var(--bg); }
[hidden] { display: none !important; }
button, input, select, textarea { font: inherit; }
button, .primary, .secondary, input:not([type="checkbox"]), select { min-height: 48px; }
button:disabled { opacity: .45; cursor: default; }
button, a, input, select, textarea, summary { -webkit-tap-highlight-color: transparent; }
a:focus-visible, button:focus-visible, input:focus-visible, select:focus-visible,
textarea:focus-visible, summary:focus-visible { outline: 2px solid var(--green); outline-offset: 3px; }
input, select, textarea, .knowledge-ask textarea { color: var(--ink); background: var(--field); border-color: var(--line); }
input::placeholder, textarea::placeholder { color: var(--muted); opacity: 1; }
.primary { background: var(--primary); color: var(--primary-text); }
.primary:hover { background: var(--primary); filter: brightness(.92); }
.secondary { color: var(--ink); background: var(--side); border: 1px solid var(--line); }
.secondary:hover { background: var(--accent); }
.text-button { color: var(--muted); min-height: 48px; }
.site-header { background: var(--side); }
.header-inner { max-width: 1320px; min-height: 72px; padding: 12px 28px; gap: 20px; }
.brand { font-size: 18px; font-weight: 650; letter-spacing: 0; }
.brand-icon { width: 34px; height: 34px; flex: 0 0 34px; object-fit: contain; background: transparent; border: 0; border-radius: 0; padding: 0; }
.brand small { letter-spacing: 2px; font-weight: 400; margin-top: 4px; }
.header-inner nav { gap: 16px; }
.header-inner nav > a { min-height: 48px; display: inline-flex; align-items: center; }
.theme-switch { padding: 8px 12px; white-space: nowrap; }
.container { max-width: 1320px; padding: 28px 28px 56px; }
h1 { font-size: 30px; font-weight: 650; letter-spacing: -.4px; }
.page-intro { padding: 8px 0 20px; }
.eyebrow { letter-spacing: 1px; }
.panel { border-radius: 8px; }
.filters { padding: 20px; margin: 8px 0 28px; }
.catalog-filters > summary { display: none; }
.course-grid { gap: 14px; }
.course-card { padding: 22px; }
.course-card:hover { border-color: var(--green); transform: none; }
.course-card h3 { font-weight: 600; }
.subject-chip, .status-chip, .shortcut-count { background: var(--accent); color: var(--green); }
.course-bottom { border-color: var(--line); }
.notice { background: var(--notice); border-color: var(--line); color: var(--ink); }
.validation, .ask-error, .math-error { color: var(--error); }
.intro-note { background: var(--accent); }
.login-wrap { gap: 64px; margin: 48px auto; }
.login-intro h1 { font-size: 44px; font-weight: 600; }
.login-card { padding: 32px; }
.site-footer { max-width: 1264px; gap: 20px; }
.appearance-notice { margin: 0 0 18px; padding: 12px 16px; background: var(--warning-bg); color: var(--warning); border-radius: 6px; }
.lesson-heading { margin: 20px 0 24px; }
.lesson-heading h1 { font-size: 30px; margin: 10px 0; }
.lesson-heading h1 span { font-size: .7em; font-weight: 400; }
.lesson-heading p { font-size: 13px; }
.lesson-layout { grid-template-columns: 220px minmax(0, 1fr); gap: 28px; }
.lesson-navigation { position: sticky; top: 16px; min-width: 0; }
.lesson-navigation > summary { display: none; }
.lesson-navigation .lesson-sidebar { position: static; }
.lesson-sidebar { top: 16px; max-height: calc(100dvh - 32px); gap: 12px; }
.lesson-nav { padding: 18px; gap: 8px; background: var(--side); }
.lesson-nav > a { min-height: 48px; display: flex; align-items: center; }
.lesson-nav > button { padding: 0; }
.lesson-nav strong { font-weight: 600; }
.course-shortcuts { padding: 0 14px; background: var(--side); }
.shortcut-course:hover, .branch-link:hover { background: var(--accent); }
.shortcut-course.is-current, .branch-link[aria-current="location"] { background: var(--accent); border-color: var(--line); color: var(--green); }
.summary, .study-reading { background: transparent; border: 0; border-radius: 0; padding: 24px 32px 40px; max-width: 884px; margin: 0 auto; }
.article-label { padding-bottom: 14px; margin-bottom: 24px; }
.markdown, .study-reading .markdown {
    font-family: "Noto Sans SC", "Microsoft YaHei UI", "PingFang SC", sans-serif;
    font-size: var(--reading-font-size);
    line-height: 1.9;
    font-weight: 400;
}
.markdown h1 { font-size: 1.75em; font-weight: 600; }
.markdown h2 { font-size: 1.3em; font-weight: 600; margin: 1.7em 0 .7em; }
.markdown h3, .study-reading .markdown h3 { font-size: 1.12em; font-weight: 600; margin-top: 1.5em; }
.markdown p { margin: .9em 0; }
.markdown li { margin: .3em 0; }
.markdown pre, .markdown code, .transcript, .selection-preview { background: var(--paper); }
.markdown pre { border: 1px solid var(--line); font-size: .85em; }
.markdown pre code { background: transparent; padding: 0; }
.markdown blockquote { margin: 1.2em 0; padding: .2em 1em; border-left: 3px solid var(--green); color: var(--muted); }
.markdown th { background: var(--paper); }
.attachments { background: var(--side); }
.knowledge-nav, .knowledge-card { background: var(--side); }
.knowledge-card:target { border-color: var(--green); box-shadow: 0 0 0 2px var(--accent); }
.study-page { max-width: 948px; }
.study-heading h1 { font-size: 30px; }
.study-toolbar { align-items: center; }
.reader-toolbar { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin: 0 0 16px; padding: 10px 0; border-bottom: 1px solid var(--line); background: var(--bg); }
.reader-font-controls, .reader-view-controls { display: flex; align-items: center; gap: 8px; }
.reader-view-controls { flex-wrap: wrap; justify-content: flex-end; max-width: 100%; }
.reader-font-controls > span { min-width: 54px; text-align: center; }
.reader-toolbar button { padding: 8px 14px; }
.reader-toolbar #open-exploration { color: var(--primary-text); background: var(--primary); border-radius: 8px; padding: 8px 14px; font-weight: 600; }
.reader-toolbar [aria-pressed="true"] { border-color: var(--green); background: var(--accent); }
.reading-full-width .summary, .reading-full-width .study-reading, .reading-full-width .study-page { max-width: none; }
.reading-focus .site-header, .reading-focus .site-footer, .reading-focus .back-link,
.reading-focus .lesson-heading, .reading-focus .study-heading, .reading-focus .lesson-sidebar, .reading-focus .lesson-navigation { display: none; }
.reading-focus .container { max-width: 1080px; padding-top: 0; }
.reading-focus .lesson-layout { display: block; }
.reading-focus .reader-toolbar { position: sticky; top: 0; z-index: 20; padding-top: 12px; }
.exploration-dialog { color: var(--ink); background: var(--paper); border-color: var(--line); border-radius: 10px; box-shadow: 0 16px 60px #0006; }
.exploration-heading { padding: 16px 20px; }
.exploration-heading h2 { font-size: 20px; }
.exploration-content { padding: 18px 20px; }
.knowledge-branch .markdown { font-size: max(15px, calc(var(--reading-font-size) - 2px)); }
.knowledge-branch .markdown h1, .knowledge-branch .markdown h2 { font-size: 1.18em; }
.provider-badge { color: var(--green); background: var(--accent); }
.provider-badge.simulated { color: var(--warning); background: var(--warning-bg); }
.selection-tools { background: var(--paper); border-color: var(--line); box-shadow: 0 8px 28px #0006; }
.branch-link, .knowledge-ask textarea, .knowledge-ask select { color: var(--ink); }
.branch-navigation-heading button, .exploration-dialog button { min-height: 48px; }
.knowledge-ask textarea { min-height: 112px; }
.ask-footer > button { min-height: 48px; }
@media (max-width: 950px) {
    .lesson-layout { grid-template-columns: 190px minmax(0, 1fr); gap: 18px; }
    .header-inner { gap: 12px; }
    .header-inner nav { gap: 10px; }
    .summary, .study-reading { padding: 20px 18px 32px; }
}
@media (max-width: 650px) {
    .header-inner { padding: 10px 16px; min-height: 68px; align-items: center; flex-wrap: wrap; }
    .brand { font-size: 17px; }
    .header-inner nav { flex: 1; font-size: 13px; gap: 8px 12px; }
    .header-inner nav.admin-navigation { flex-basis: 100%; justify-content: flex-start; }
    .header-inner nav .small { font-size: 12px; }
    .theme-switch { padding: 8px 10px; }
    .container { padding: 20px 16px 36px; }
    h1, .lesson-heading h1, .study-heading h1 { font-size: 26px; }
    .filters { padding: 16px; gap: 12px; }
    .filters > div:first-child { flex-basis: 100%; }
    .catalog-filters { margin: 0 0 24px; }
    .catalog-filters > summary { display: flex; align-items: center; justify-content: space-between; gap: 12px; min-height: 48px; padding: 10px 14px; border: 1px solid var(--line); border-radius: 6px; background: var(--side); cursor: pointer; }
    .catalog-filters .filters { margin-bottom: 0; }
    .lesson-layout { display: block; }
    .lesson-navigation { position: static; margin-bottom: 16px; }
    .lesson-navigation > summary { display: flex; align-items: center; min-height: 48px; padding: 10px 14px; border: 1px solid var(--line); border-radius: 6px; background: var(--side); cursor: pointer; }
    .lesson-navigation[open] > summary { margin-bottom: 12px; }
    .lesson-sidebar { position: static; max-height: none; }
    .lesson-nav { padding: 12px 16px; }
    .summary, .study-reading { padding: 20px 4px 32px; }
    .reader-toolbar { flex-wrap: wrap; gap: 8px; }
    .reader-toolbar button, .reader-toolbar #open-exploration { padding: 8px 10px; white-space: nowrap; }
    .reader-view-controls { margin-left: auto; gap: 6px; }
    .reader-font-controls > span { min-width: 48px; }
    .login-wrap { margin: 12px auto; }
    .login-card { padding: 24px; }
    .login-intro h1 { font-size: 34px; }
    .site-footer { margin: 0 16px; padding: 20px 0; }
    .exploration-dialog { border-radius: 12px 12px 0 0; }
    .exploration-content { padding: 16px; padding-bottom: max(20px, env(safe-area-inset-bottom)); }
    .reading-focus .container { padding: 0 16px 32px; }
}