/* PHP 练功房
   布局：顶栏 + 首页（开篇演示 / 学习方式 / 课程目录）；课程页左侧目录 + 右侧正文列（约 760px），
   代码编辑器统一用深色“工作台”，在浅色和深色主题下都一样。 */

@font-face {
    font-family: "JetBrains Mono";
    src: url("../vendor/fonts/jetbrains-mono-400.woff2") format("woff2");
    font-weight: 400;
    font-display: swap;
}
@font-face {
    font-family: "JetBrains Mono";
    src: url("../vendor/fonts/jetbrains-mono-700.woff2") format("woff2");
    font-weight: 700;
    font-display: swap;
}

:root {
    --bg: #F5F5F8;
    --surface: #FFFFFF;
    --ink: #1B1C29;
    --muted: #5D6077;
    --line: #DDDEE8;
    --accent: #4F5B93;
    --accent-hover: #434E82;
    --accent-ink: #FFFFFF;
    --accent-soft: #E8E9F4;
    --ok: #1E7B4E;
    --ok-soft: #E3F3EA;
    --bad: #B42318;
    --bad-soft: #FBEAE7;
    --warn: #8A5A00;
    --warn-soft: #FBF1DC;

    --code-bg: #1D1F2E;
    --code-gutter: #1D1F2E;
    --code-ink: #E3E4F0;
    --code-line: #5B5F7A;
    --code-kw: #B9BFF8;
    --code-var: #7FD3C8;
    --code-str: #F0C48A;
    --code-num: #F4A3C8;
    --code-com: #7E829E;
    --code-fn: #8FC6FF;
    --code-meta: #9DA4EA;
    --code-out-bg: #F0F1F6;

    --font-sans: -apple-system, BlinkMacSystemFont, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans SC", "Source Han Sans SC", system-ui, sans-serif;
    --font-mono: "JetBrains Mono", "Cascadia Mono", Consolas, Menlo, "Microsoft YaHei", "PingFang SC", monospace;

    --radius: 10px;
    --gutter: 20px;
    color-scheme: light;
}

@media (prefers-color-scheme: dark) {
    :root {
        color-scheme: dark;
        --bg: #111219;
        --surface: #181A24;
        --ink: #E7E8F0;
        --muted: #9A9DB3;
        --line: #2A2D3C;
        --accent: #A3AAE8;
        --accent-hover: #B8BEF0;
        --accent-ink: #12131B;
        --accent-soft: #232640;
        --ok: #5CCB8E;
        --ok-soft: #16301F;
        --bad: #FF8F80;
        --bad-soft: #3A1E1B;
        --warn: #F0C064;
        --warn-soft: #332910;
        --code-bg: #0D0E15;
        --code-gutter: #0D0E15;
        --code-out-bg: #1E2030;
    }
}

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
    margin: 0;
    background: var(--bg);
    color: var(--ink);
    font: 16px/1.75 var(--font-sans);
    -webkit-font-smoothing: antialiased;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}
main { flex: 1 0 auto; }
a { color: var(--accent); text-underline-offset: 3px; }
a:hover { color: var(--accent-hover); }
img { max-width: 100%; }
[hidden] { display: none !important; }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
code, kbd, pre, .CodeMirror { font-family: var(--font-mono); font-variant-ligatures: none; font-feature-settings: "liga" 0, "calt" 0; }
kbd {
    font-size: 0.8em;
    padding: 0.05em 0.4em;
    border: 1px solid var(--line);
    border-bottom-width: 2px;
    border-radius: 4px;
    background: var(--surface);
}
h1, h2, h3, h4 { text-wrap: balance; line-height: 1.3; }

/* ---------- 按钮 ---------- */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 6px;
    min-height: 36px;
    padding: 0 14px;
    border: 1px solid var(--line);
    border-radius: 8px;
    background: var(--surface);
    color: var(--ink);
    font: 500 14px/1 var(--font-sans);
    text-decoration: none;
    cursor: pointer;
    white-space: nowrap;
    transition: background-color 0.15s, border-color 0.15s;
}
.btn:hover { border-color: var(--accent); color: var(--ink); }
.btn:disabled { opacity: 0.55; cursor: default; }
.btn-primary { background: var(--accent); border-color: var(--accent); color: var(--accent-ink); }
.btn-primary:hover { background: var(--accent-hover); border-color: var(--accent-hover); color: var(--accent-ink); }
.btn-quiet { background: transparent; border-color: transparent; color: var(--muted); }
.btn-quiet:hover { color: var(--ink); border-color: var(--line); }
.btn-lg { min-height: 46px; padding: 0 22px; font-size: 16px; border-radius: 10px; }
.btn-block { width: 100%; min-height: 44px; font-size: 15px; }
.btn-run { background: #3FA86B; border-color: #3FA86B; color: #fff; }
.btn-run:hover { background: #359160; border-color: #359160; color: #fff; }
.inline-form { display: inline; margin: 0; }

/* ---------- 顶栏 ---------- */
.topbar {
    position: sticky;
    top: 0;
    z-index: 20;
    padding-top: env(safe-area-inset-top, 0px);
    background: color-mix(in srgb, var(--bg) 88%, transparent);
    backdrop-filter: saturate(1.4) blur(10px);
    border-bottom: 1px solid var(--line);
}
.topbar-inner {
    max-width: 1180px;
    margin: 0 auto;
    padding: 0 var(--gutter);
    height: 58px;
    display: flex;
    align-items: center;
    gap: 28px;
}
.brand { display: flex; align-items: baseline; gap: 6px; text-decoration: none; color: var(--ink); }
.brand:hover { color: var(--ink); }
.brand-tag { font: 700 15px/1 var(--font-mono); color: var(--accent); letter-spacing: -0.02em; }
.brand-name { font-weight: 700; font-size: 17px; letter-spacing: 0.04em; }
.nav { display: flex; gap: 20px; }
.nav a { color: var(--muted); text-decoration: none; font-size: 15px; }
.nav a:hover { color: var(--ink); }
.account { margin-left: auto; display: flex; align-items: center; gap: 8px; }
.account-name { font-size: 14px; color: var(--muted); max-width: 10em; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }

/* ---------- 首页 ---------- */
.home { max-width: 1180px; margin: 0 auto; padding: 56px var(--gutter) 80px; width: 100%; }
.hero {
    display: grid;
    grid-template-columns: minmax(0, 1fr) minmax(0, 1.1fr);
    gap: 56px;
    align-items: start;
}
.hero-copy { padding-top: 24px; }
.eyebrow { margin: 0 0 12px; font-size: 13px; letter-spacing: 0.08em; color: var(--muted); }
.hero h1 { font-size: clamp(40px, 6vw, 64px); line-height: 1.1; margin: 0 0 20px; letter-spacing: 0.02em; font-weight: 800; }
.lede { font-size: 18px; color: var(--muted); margin: 0 0 28px; max-width: 32em; }
.lede code { font-size: 0.9em; color: var(--ink); background: var(--accent-soft); padding: 0.1em 0.4em; border-radius: 4px; }
.hero-actions { display: flex; flex-wrap: wrap; gap: 12px; }
.hero-progress { margin: 18px 0 0; font-size: 14px; color: var(--muted); }
.hero-demo-note { margin: 10px 2px 0; font-size: 13px; color: var(--muted); }

.how {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 32px;
    margin: 80px 0 72px;
    padding: 28px 0;
    border-top: 1px solid var(--line);
    border-bottom: 1px solid var(--line);
}
.how h2 { font-size: 17px; margin: 0 0 6px; }
.how p { margin: 0; color: var(--muted); font-size: 15px; }

.course-head { display: flex; align-items: baseline; justify-content: space-between; gap: 16px; flex-wrap: wrap; margin-bottom: 28px; }
.course-head h2 { font-size: 28px; margin: 0; }
.course-meta { margin: 0; color: var(--muted); font-size: 14px; }
.chapters { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 40px 48px; }
.chapter h3 { margin: 0 0 10px; font-size: 18px; display: flex; gap: 10px; align-items: baseline; }
.chapter-no { font: 700 13px/1 var(--font-mono); color: var(--accent); letter-spacing: 0.04em; }
.lesson-links { list-style: none; margin: 0; padding: 0; display: grid; gap: 2px; }
.lesson-link {
    display: grid;
    grid-template-columns: 18px 2.6em minmax(0, 1fr) auto;
    gap: 10px;
    align-items: baseline;
    padding: 10px 10px;
    margin: 0 -10px;
    border-radius: 8px;
    text-decoration: none;
    color: var(--ink);
}
.lesson-link:hover { background: var(--surface); color: var(--ink); }
.lesson-num { font: 500 13px/1 var(--font-mono); color: var(--muted); font-variant-numeric: tabular-nums; }
.lesson-text { display: grid; gap: 2px; min-width: 0; }
.lesson-title { font-weight: 600; }
.lesson-sum { font-size: 13.5px; color: var(--muted); line-height: 1.5; }
.lesson-min { font-size: 12.5px; color: var(--muted); white-space: nowrap; font-variant-numeric: tabular-nums; }
.lesson-status {
    width: 12px;
    height: 12px;
    border-radius: 50%;
    border: 1.5px solid var(--line);
    align-self: center;
}
.lesson-link[data-status="started"] .lesson-status { border-color: var(--accent); background: linear-gradient(90deg, var(--accent) 50%, transparent 50%); }
.lesson-link[data-status="done"] .lesson-status { border-color: var(--ok); background: var(--ok); box-shadow: inset 0 0 0 2px var(--bg); }

/* ---------- 编辑器（CodeMirror 主题 plf） ---------- */
.example, .exercise-editor {
    border-radius: var(--radius);
    overflow: hidden;
    background: var(--code-bg);
    border: 1px solid color-mix(in srgb, var(--code-bg) 70%, var(--line));
}
.example + .example { margin-top: 20px; }
.CodeMirror {
    height: auto;
    font: 14px/1.65 var(--font-mono);
    background: var(--code-bg);
    color: var(--code-ink);
    padding: 10px 0;
}
.CodeMirror-scroll { min-height: 3em; }
.CodeMirror-gutters { background: var(--code-gutter); border-right: 0; }
.CodeMirror-linenumber { color: var(--code-line); padding: 0 12px 0 8px; min-width: 24px; }
.CodeMirror-cursor { border-left: 2px solid #F5F6FF; }
.CodeMirror-selected { background: rgba(140, 148, 220, 0.28) !important; }
.CodeMirror-focused .CodeMirror-selected { background: rgba(140, 148, 220, 0.38) !important; }
.CodeMirror-activeline-background { background: rgba(255, 255, 255, 0.045); }
.CodeMirror-matchingbracket { color: #fff !important; outline: 1px solid rgba(255, 255, 255, 0.4); }
.cm-error-line { background: rgba(255, 99, 88, 0.16); }
.cm-s-plf .cm-keyword, .cm-s-plf .cm-type { color: var(--code-kw); }
.cm-s-plf .cm-variable-2, .cm-s-plf .cm-variable-3 { color: var(--code-var); }
.cm-s-plf .cm-variable { color: var(--code-ink); }
.cm-s-plf .cm-def, .cm-s-plf .cm-builtin { color: var(--code-fn); }
.cm-s-plf .cm-string, .cm-s-plf .cm-string-2 { color: var(--code-str); }
.cm-s-plf .cm-number, .cm-s-plf .cm-atom { color: var(--code-num); }
.cm-s-plf .cm-comment { color: var(--code-com); font-style: italic; }
.cm-s-plf .cm-meta { color: var(--code-meta); }
.cm-s-plf .cm-tag, .cm-s-plf .cm-bracket { color: var(--code-meta); }
.cm-s-plf .cm-attribute, .cm-s-plf .cm-property { color: var(--code-fn); }
.cm-s-plf .cm-operator { color: #C8CAE0; }

.example-bar, .exercise-actions {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 8px;
    padding: 10px 12px;
    background: var(--code-bg);
    border-top: 1px solid rgba(255, 255, 255, 0.07);
}
.example-bar .btn-quiet { color: #A7AAC4; }
.example-bar .btn-quiet:hover { color: #fff; border-color: rgba(255, 255, 255, 0.2); }
.kbd-hint { margin-left: auto; font-size: 12px; color: #8D90AB; }
.kbd-hint kbd { background: transparent; border-color: #454862; color: #C9CBE0; }
.engine-note { font-size: 12.5px; color: #A7AAC4; }
.engine-note[data-state="error"] { color: #FF9C8F; }

.run-panel {
    background: var(--code-out-bg);
    color: var(--ink);
    padding: 12px 16px 14px;
    border-top: 1px solid var(--line);
}
.run-status { margin: 0 0 8px; font-size: 13px; font-weight: 600; }
.run-status.is-ok { color: var(--ok); }
.run-status.is-warn { color: var(--warn); }
.run-status.is-bad { color: var(--bad); }
.run-out {
    margin: 0;
    font: 14px/1.6 var(--font-mono);
    white-space: pre-wrap;
    word-break: break-word;
    max-height: 420px;
    overflow: auto;
}
.run-out.is-empty { color: var(--muted); }
.run-preview { width: 100%; min-height: 160px; border: 1px solid var(--line); border-radius: 6px; background: #fff; }
.tabs { display: flex; gap: 4px; margin-bottom: 8px; }
.tab {
    font: 500 12.5px/1 var(--font-sans);
    padding: 6px 10px;
    border-radius: 6px;
    border: 1px solid var(--line);
    background: transparent;
    color: var(--muted);
    cursor: pointer;
}
.tab.is-on { background: var(--surface); color: var(--ink); border-color: var(--accent); }

.err-list { list-style: none; margin: 10px 0 0; padding: 0; display: grid; gap: 8px; }
.err { padding: 10px 12px; border-radius: 8px; background: var(--warn-soft); }
.err.is-severe { background: var(--bad-soft); }
.err-head { margin: 0; display: flex; flex-wrap: wrap; align-items: baseline; gap: 8px; font-size: 13.5px; }
.err-level { font-weight: 700; color: var(--warn); }
.err.is-severe .err-level { color: var(--bad); }
.err-line {
    font: 600 12.5px/1 var(--font-sans);
    border: 0;
    background: var(--surface);
    color: var(--ink);
    padding: 4px 7px;
    border-radius: 5px;
    cursor: pointer;
}
.err-msg { font-size: 12.5px; word-break: break-word; color: var(--ink); }
.err-hint { margin: 6px 0 0; font-size: 14px; }

/* ---------- 课程页 ---------- */
.lesson-page {
    max-width: 1180px;
    margin: 0 auto;
    padding: 40px var(--gutter) 80px;
    width: 100%;
    display: grid;
    grid-template-columns: 250px minmax(0, 780px);
    gap: 56px;
    justify-content: center;
}
.lesson-nav { position: sticky; top: calc(58px + env(safe-area-inset-top, 0px) + 24px); align-self: start; max-height: calc(100vh - 110px); overflow-y: auto; overflow-x: hidden; padding-right: 4px; }
.toc summary { font-weight: 700; font-size: 14px; cursor: pointer; margin-bottom: 8px; list-style: none; }
.toc summary::-webkit-details-marker { display: none; }
.toc-chapter { margin: 16px 0 4px; font-size: 12.5px; color: var(--muted); letter-spacing: 0.04em; }
.toc-list { list-style: none; margin: 0; padding: 0; }
.toc .lesson-link { grid-template-columns: 14px 2.4em minmax(0, 1fr); gap: 8px; padding: 6px 10px; margin: 0; font-size: 14px; }
.toc .lesson-title { font-weight: 400; }
.toc .lesson-status { width: 10px; height: 10px; }
.toc .lesson-link.is-current { background: var(--accent-soft); }
.toc .lesson-link.is-current .lesson-title { font-weight: 600; }

.lesson-head { margin-bottom: 28px; }
.lesson-head h1 { font-size: clamp(30px, 4vw, 40px); margin: 0 0 12px; }
.lesson-meta { display: flex; flex-wrap: wrap; align-items: center; gap: 8px 18px; margin: 0; font-size: 13.5px; color: var(--muted); }
.lesson-meter { display: inline-flex; flex-wrap: wrap; align-items: center; gap: 8px 12px; }
.meter-bar { width: 120px; height: 6px; border-radius: 3px; background: var(--line); overflow: hidden; }
.meter-fill { display: block; height: 100%; background: var(--ok); transition: width 0.3s; }
.meter-text { font-variant-numeric: tabular-nums; color: var(--ink); }
.sync { font-size: 12.5px; }
.sync-error { color: var(--bad); }

.lesson-body { display: flex; flex-direction: column; gap: 22px; }
.prose > :first-child { margin-top: 0; }
.prose > :last-child { margin-bottom: 0; }
.prose p, .prose ul, .prose ol { margin: 0 0 14px; max-width: 42em; }
.prose h3 { font-size: 21px; margin: 18px 0 10px; }
.prose h4 { font-size: 17px; margin: 14px 0 8px; }
.prose ul, .prose ol { padding-left: 1.4em; }
.prose li + li { margin-top: 4px; }
.prose code, .quiz code, .tip code, .hints code, .check code {
    font-size: 0.88em;
    background: var(--accent-soft);
    color: var(--ink);
    padding: 0.12em 0.4em;
    border-radius: 4px;
    word-break: break-word;
}
.table-wrap { overflow-x: auto; margin: 0 0 14px; }
.prose table { border-collapse: collapse; font-size: 14.5px; min-width: 60%; }
.prose th, .prose td { text-align: left; padding: 8px 16px 8px 0; border-bottom: 1px solid var(--line); vertical-align: top; }
.prose th { font-size: 13px; color: var(--muted); font-weight: 600; }
pre.static-code {
    margin: 0 0 14px;
    padding: 14px 16px;
    background: var(--code-bg);
    color: var(--code-ink);
    border-radius: 8px;
    font: 14px/1.6 var(--font-mono);
    overflow-x: auto;
}
pre.static-code code { background: none; padding: 0; color: inherit; font-size: inherit; }

.tip {
    padding: 14px 18px;
    border-radius: var(--radius);
    background: var(--accent-soft);
    font-size: 15px;
}
.tip p { margin: 0; }
.tip p + p { margin-top: 8px; }

.block-label { margin: 0 0 6px; font: 700 12px/1 var(--font-sans); letter-spacing: 0.1em; color: var(--accent); }

.quiz {
    padding: 20px 22px;
    border: 1px solid var(--line);
    border-radius: var(--radius);
    background: var(--surface);
}
.quiz-q { margin: 0 0 12px; font-weight: 600; }
.quiz-options { display: grid; gap: 8px; }
.quiz-opt {
    display: flex;
    gap: 12px;
    align-items: baseline;
    text-align: left;
    padding: 10px 14px;
    border: 1px solid var(--line);
    border-radius: 8px;
    background: var(--bg);
    color: var(--ink);
    font: 15px/1.6 var(--font-sans);
    cursor: pointer;
}
.quiz-opt:hover:not(:disabled) { border-color: var(--accent); }
.quiz-opt:disabled { cursor: default; }
.opt-key { font: 700 13px/1 var(--font-mono); color: var(--muted); }
.quiz-opt.is-right { border-color: var(--ok); background: var(--ok-soft); }
.quiz-opt.is-right .opt-key { color: var(--ok); }
.quiz-opt.is-wrong { border-color: var(--bad); background: var(--bad-soft); opacity: 0.8; }
.quiz-feedback { margin-top: 12px; font-size: 15px; }
.quiz-feedback.is-right strong { color: var(--ok); }
.quiz-feedback.is-wrong { color: var(--bad); }

.exercise {
    padding: 22px 22px 20px;
    border: 1px solid var(--line);
    border-radius: 14px;
    background: var(--surface);
    display: flex;
    flex-direction: column;
    gap: 14px;
}
.exercise.is-passed { border-color: color-mix(in srgb, var(--ok) 45%, var(--line)); }
.exercise-head { display: flex; flex-wrap: wrap; align-items: baseline; gap: 4px 12px; }
.exercise-head .block-label { flex-basis: 100%; }
.exercise-head h2 { margin: 0; font-size: 20px; }
.ex-badge { font-size: 12.5px; font-weight: 700; color: var(--ok); background: var(--ok-soft); padding: 3px 9px; border-radius: 999px; }
.exercise-editor { display: flex; flex-direction: column; }
.exercise-actions { border-radius: 0 0 var(--radius) var(--radius); margin-top: -14px; }
.exercise-actions .btn-quiet { color: #A7AAC4; }
.exercise-actions .btn-quiet:hover { color: #fff; border-color: rgba(255, 255, 255, 0.2); }
.exercise-actions .btn:not(.btn-primary):not(.btn-quiet) { background: transparent; color: #E3E4F0; border-color: #454862; }
.exercise-actions .btn:not(.btn-primary):not(.btn-quiet):hover { border-color: #9DA4EA; }
.exercise-actions .btn-primary { background: #3FA86B; border-color: #3FA86B; color: #fff; }
.exercise-actions .btn-primary:hover { background: #359160; border-color: #359160; }
.spacer { flex: 1; }
.exercise-feedback:empty { display: none; }
.exercise-feedback .run-panel { border: 1px solid var(--line); border-radius: var(--radius); }

.check { border-radius: var(--radius); padding: 14px 16px; border: 1px solid var(--line); }
.check.is-pass { background: var(--ok-soft); border-color: color-mix(in srgb, var(--ok) 35%, transparent); }
.check.is-fail { background: var(--surface); }
.check-title { margin: 0 0 10px; font-weight: 700; }
.check.is-pass .check-title { color: var(--ok); }
.check.is-fail .check-title { color: var(--bad); }
.check-list { list-style: none; margin: 0; padding: 0; display: grid; gap: 8px; }
.check-list > li { display: grid; grid-template-columns: 18px minmax(0, 1fr); gap: 4px 8px; font-size: 14.5px; }
.check-mark { font-weight: 700; }
.is-ok > .check-mark { color: var(--ok); }
.is-bad > .check-mark { color: var(--bad); }
.check-detail { grid-column: 2; display: grid; gap: 8px; }
.check-detail p { margin: 0; }
.check-setup { font-size: 13.5px; color: var(--muted); }
.diff { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 10px; }
.diff-label { font-size: 12px; color: var(--muted); margin: 0 0 4px !important; }
.diff pre {
    margin: 0;
    padding: 8px 10px;
    background: var(--code-out-bg);
    border-radius: 6px;
    font: 13px/1.55 var(--font-mono);
    white-space: pre-wrap;
    word-break: break-word;
    max-height: 240px;
    overflow: auto;
}
.check-nudge { margin: 12px 0 0; font-size: 14px; color: var(--muted); }
.restored { margin: 0; font-size: 13.5px; color: var(--muted); }

.hints { margin: 0; padding: 12px 16px 12px 2.2em; background: var(--warn-soft); border-radius: var(--radius); font-size: 15px; display: grid; gap: 6px; }
.solution { padding: 14px 16px; border: 1px dashed var(--line); border-radius: var(--radius); display: grid; gap: 10px; }
.solution p { margin: 0; }
.solution pre.static-code { margin: 0; }
.solution-title { font-weight: 700; font-size: 14px; }
.solution-actions { display: flex; gap: 8px; }

.lesson-foot { margin-top: 48px; display: grid; gap: 24px; }
.lesson-done { padding: 18px 20px; border-radius: 14px; background: var(--ok-soft); }
.lesson-done p { margin: 0; }
.lesson-done-title { font-weight: 800; font-size: 18px; color: var(--ok); margin-bottom: 4px !important; }
.pager { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.pager-link {
    display: grid;
    gap: 2px;
    padding: 14px 18px;
    border: 1px solid var(--line);
    border-radius: var(--radius);
    background: var(--surface);
    text-decoration: none;
    color: var(--ink);
    font-weight: 600;
}
.pager-link:hover { border-color: var(--accent); color: var(--ink); }
.pager-next { text-align: right; }
.pager-dir { font-size: 12.5px; font-weight: 400; color: var(--muted); }

/* ---------- 自由练习 ---------- */
.playground { max-width: 980px; margin: 0 auto; padding: 40px var(--gutter) 80px; width: 100%; }
.playground-head h1 { margin: 0 0 6px; font-size: 32px; }
.playground-head p { margin: 0 0 22px; color: var(--muted); }
.example-playground .CodeMirror-scroll { min-height: 320px; }

/* ---------- 登录注册 ---------- */
.auth { display: grid; place-items: start center; padding: 56px var(--gutter) 80px; }
.auth-card {
    width: 100%;
    max-width: 400px;
    padding: 32px 30px;
    background: var(--surface);
    border: 1px solid var(--line);
    border-radius: 16px;
    display: flex;
    flex-direction: column;
    gap: 8px;
}
.auth-card h1 { margin: 0; font-size: 26px; }
.auth-sub { margin: 0 0 10px; color: var(--muted); font-size: 14.5px; }
.auth-card label { font-size: 14px; font-weight: 600; margin-top: 8px; }
.auth-card input {
    height: 44px;
    padding: 0 12px;
    border: 1px solid var(--line);
    border-radius: 8px;
    background: var(--bg);
    color: var(--ink);
    font: 16px var(--font-sans);
}
.auth-card input:focus { border-color: var(--accent); outline: none; box-shadow: 0 0 0 3px var(--accent-soft); }
.auth-card .btn-block { margin-top: 16px; }
.field-hint { margin: 0; font-size: 12.5px; color: var(--muted); }
.form-error { margin: 0 0 6px; padding: 10px 12px; border-radius: 8px; background: var(--bad-soft); color: var(--bad); font-size: 14px; }
.auth-switch { margin: 10px 0 0; font-size: 14px; color: var(--muted); text-align: center; }
.hp { position: absolute; left: -9999px; width: 1px; height: 1px; overflow: hidden; }

.narrow { max-width: 640px; margin: 0 auto; padding: 64px var(--gutter); }

/* ---------- 页脚 ---------- */
.footer { border-top: 1px solid var(--line); padding-bottom: env(safe-area-inset-bottom, 0px); }
.footer-inner {
    max-width: 1180px;
    margin: 0 auto;
    padding: 22px var(--gutter);
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
    gap: 8px 24px;
    font-size: 13px;
    color: var(--muted);
}
.footer p { margin: 0; }
.footer .brand-tag { font-size: 12px; }

/* ---------- 响应式 ---------- */
@media (max-width: 980px) {
    .hero { grid-template-columns: minmax(0, 1fr); gap: 36px; }
    .chapters { grid-template-columns: minmax(0, 1fr); }
    .lesson-page { grid-template-columns: minmax(0, 1fr); gap: 20px; padding-top: 24px; }
    .lesson-nav { position: static; max-height: none; overflow: visible; }
    .toc { border: 1px solid var(--line); border-radius: var(--radius); padding: 10px 14px; background: var(--surface); }
    .toc summary { margin: 0; }
    .toc[open] summary { margin-bottom: 8px; }
}
@media (max-width: 640px) {
    :root { --gutter: 16px; }
    .topbar-inner { gap: 14px; }
    .nav { gap: 14px; }
    .nav a { font-size: 14px; }
    .account .btn { padding: 0 10px; }
    .account-name { display: none; }
    .home { padding-top: 36px; }
    .how { grid-template-columns: minmax(0, 1fr); gap: 18px; margin: 48px 0; }
    .lesson-link { grid-template-columns: 14px 2.4em minmax(0, 1fr); }
    .lesson-min { display: none; }
    .exercise { padding: 16px 14px; }
    .diff { grid-template-columns: minmax(0, 1fr); }
    .kbd-hint { display: none; }
    .CodeMirror { font-size: 13px; }
    .pager { grid-template-columns: minmax(0, 1fr); }
    .pager-next { text-align: left; }
}
@media (max-width: 400px) {
    .brand-name { display: none; }
}
@media (prefers-reduced-motion: reduce) {
    * { transition: none !important; }
}