/* ===== 计算机音乐互动课堂 · 商业交付版 UI ===== */
:root{
  color-scheme:light;
  --bg:#f4f7fb;
  --bg-deep:#edf2f8;
  --card:#ffffff;
  --card-soft:#f8fafc;
  --text:#172033;
  --text-2:#46536a;
  --muted:#5f6c82;
  --accent:#356ee6;
  --accent-strong:#2458c7;
  --accent-soft:#edf3ff;
  --teal:#128f86;
  --teal-soft:#eaf8f6;
  --warn:#b45820;
  --warn-soft:#fff5eb;
  --success:#27845a;
  --success-soft:#ecf8f2;
  --line:#dfe6ef;
  --line-soft:#eaf0f6;
  --shadow-sm:0 1px 2px rgba(20,35,60,.05),0 4px 14px rgba(33,53,86,.05);
  --shadow-md:0 12px 34px rgba(35,55,88,.10);
  --shadow-lg:0 26px 70px rgba(38,61,100,.14);
  --radius-xl:26px;
  --radius-lg:20px;
  --radius-md:14px;
  --radius-sm:10px;
  --sidebar-w:292px;
  --content-w:820px;
}

*{box-sizing:border-box;margin:0;padding:0}
html{scroll-behavior:smooth;-webkit-font-smoothing:antialiased;text-rendering:optimizeLegibility}
body{
  min-height:100vh;
  background:
    radial-gradient(circle at 50% -10%,rgba(72,121,232,.10),transparent 34rem),
    linear-gradient(180deg,#f8faff 0,#f4f7fb 34rem,#f4f7fb 100%);
  color:var(--text);
  font-family:-apple-system,BlinkMacSystemFont,"SF Pro Text","PingFang SC","Microsoft YaHei","Helvetica Neue",Arial,sans-serif;
  font-size:16px;
  line-height:1.72;
  letter-spacing:-.006em;
}
button,input,select{font:inherit}
button{color:inherit}
a{color:inherit}
svg{display:block}
::selection{background:rgba(53,110,230,.16)}

.skip-link{
  position:fixed;left:16px;top:10px;z-index:200;transform:translateY(-180%);
  padding:9px 14px;border-radius:10px;background:var(--text);color:#fff;text-decoration:none;
  transition:transform .2s ease;
}
.skip-link:focus{transform:none}

/* ---------- 首屏 ---------- */
.hero{
  position:relative;overflow:hidden;padding:62px 24px 42px;text-align:center;
  border-bottom:1px solid rgba(216,226,239,.76);
}
.hero-inner{position:relative;z-index:2;max-width:860px;margin:0 auto}
.hero-glow{position:absolute;border-radius:50%;filter:blur(4px);pointer-events:none}
.hero-glow-a{width:380px;height:380px;left:-150px;top:-210px;background:rgba(74,131,239,.12)}
.hero-glow-b{width:320px;height:320px;right:-120px;top:-190px;background:rgba(31,177,165,.10)}
.brand-mark{width:76px;height:76px;margin:0 auto 18px}
.brand-mark svg{width:100%;height:100%}
.hero h1{font-size:clamp(36px,5vw,54px);line-height:1.12;font-weight:780;letter-spacing:-.045em}

/* 语言选择器（视口最顶右，固定定位） */
.lang-wrap{position:fixed;top:12px;right:14px;z-index:100}
.lang-btn{display:flex;align-items:center;gap:6px;padding:7px 13px;border:1px solid var(--line);border-radius:10px;background:rgba(255,255,255,.82);color:var(--text-2);font-size:13px;font-weight:600;cursor:pointer;box-shadow:var(--shadow-sm)}
.lang-btn:hover{border-color:var(--accent);color:var(--accent-strong)}
.lang-menu{position:absolute;top:calc(100% + 6px);right:0;min-width:150px;background:#fff;border:1px solid var(--line);border-radius:12px;box-shadow:0 10px 30px rgba(20,35,60,.14);overflow:hidden;z-index:30}
.lang-menu button{display:block;width:100%;text-align:left;padding:10px 16px;border:none;background:transparent;color:var(--text-2);font-size:14px;cursor:pointer}
.lang-menu button:hover{background:var(--accent-soft);color:var(--accent-strong)}
.lang-menu button.active{font-weight:700;color:var(--accent-strong);background:var(--accent-soft)}

/* ---------- 应用布局 ---------- */
.layout{display:grid;grid-template-columns:var(--sidebar-w) minmax(0,var(--content-w));justify-content:center;gap:34px;align-items:start;max-width:1210px;margin:0 auto;padding:38px 24px 80px}
.sidebar{position:sticky;top:18px;max-height:calc(100vh - 36px);overflow:auto;border:1px solid var(--line);border-radius:var(--radius-lg);background:rgba(255,255,255,.92);box-shadow:var(--shadow-sm);backdrop-filter:blur(14px);scrollbar-width:thin}
.sidebar-head{display:flex;align-items:flex-start;justify-content:space-between;padding:20px 20px 14px;border-bottom:1px solid var(--line-soft)}
.sidebar-head h2{font-size:19px;line-height:1.25;letter-spacing:-.025em}
.sidebar-note{margin-top:5px;color:var(--muted);font-size:11.5px;line-height:1.45}
.sidebar-close{display:none;width:36px;height:36px;border:0;border-radius:10px;background:var(--card-soft);cursor:pointer;align-items:center;justify-content:center}
.sidebar-close svg,.menu-btn svg{width:20px;height:20px;fill:none;stroke:currentColor;stroke-width:1.9;stroke-linecap:round}
#courseNav{padding:10px 10px 14px}
.nav-item{
  position:relative;display:grid;grid-template-columns:30px minmax(0,1fr);align-items:center;gap:6px;width:100%;
  margin:2px 0;padding:9px 10px;border:0;border-radius:10px;background:transparent;text-align:left;cursor:pointer;
  color:var(--text-2);font-size:13.5px;line-height:1.42;transition:background .14s ease,color .14s ease;
}
.nav-item:hover{background:#f3f6fa;color:var(--text)}
.nav-item.active{background:var(--accent-soft);color:var(--accent-strong);font-weight:650}
.nav-num{color:#7e8ba0;font-size:11px;font-variant-numeric:tabular-nums}
.nav-item.active .nav-num{color:var(--accent)}

.panels{min-width:0;outline:none}
.panel{display:none;animation:panelIn .28s ease both}
.panel.active{display:block}
@keyframes panelIn{from{opacity:0;transform:translateY(7px)}to{opacity:1;transform:none}}
.chapter-head{margin-bottom:20px;padding:3px 2px}
.chapter-meta{display:flex;align-items:center;gap:9px;margin-bottom:8px;color:var(--muted);font-size:12px;font-weight:650}
.chapter-meta .dot{width:3px;height:3px;border-radius:50%;background:#a8b2c2}
.chapter-head h2{font-size:clamp(28px,4vw,38px);line-height:1.18;letter-spacing:-.04em;font-weight:760}

/* ---------- 内容卡片 ---------- */
.block{position:relative;margin-bottom:15px;padding:25px 28px;border:1px solid var(--line-soft);border-radius:var(--radius-lg);background:var(--card);box-shadow:0 1px 2px rgba(20,35,60,.035)}
.block p{margin-bottom:11px;color:var(--text-2);font-size:15.5px}
.block p:last-child{margin-bottom:0}
.block-title{display:flex;align-items:center;gap:10px;margin-bottom:15px;color:var(--text);font-size:16px;font-weight:720;letter-spacing:-.012em}
.ic{display:inline-grid;width:25px;height:25px;flex:0 0 25px;place-items:center}
.ic svg{width:21px;height:21px}
.ic-why,.ic-lesson,.ic-demo{color:var(--accent)}
.ic-hist{color:var(--teal)}
.ic-listen{color:var(--teal)}
.ic-check{color:var(--success)}
.ic-pitfall{color:var(--warn)}
.block.intro{padding:28px;background:linear-gradient(145deg,#fff 0%,#f4f8ff 100%);border-color:#dce7f7}
.block.intro .one-line{margin-bottom:14px;color:var(--text);font-size:18px;line-height:1.68;font-weight:600}
.block.lesson{border-left:3px solid #d7e4ff}
.block.pitfall{background:var(--warn-soft);border-color:#f2dac8}
.block.listen{background:var(--teal-soft);border-color:#d5eee9}
.block.check{background:var(--success-soft);border-color:#d8ede2}
.block.case{background:#fff}
.case-grid{display:grid;gap:9px}
.case-item{padding:14px 15px;border:1px solid var(--line-soft);border-radius:12px;background:var(--card-soft);font-size:14.5px;color:var(--text-2)}
.case-item>strong{display:block;margin-bottom:4px;color:var(--accent-strong)}
.block.links .link-list{list-style:none;padding:0}
.block.links .link-list li{padding:9px 0;border-bottom:1px dashed var(--line-soft)}
.block.links .link-list li:last-child{border-bottom:none}
.block.links .link-list a{color:var(--accent-strong);font-weight:620;text-decoration:none}
.block.links .link-list a:hover{text-decoration:underline}
.block.links .link-list span{display:block;margin-top:2px;font-size:13px;color:var(--muted)}
.reflection-list{display:grid;gap:8px;padding-left:1.2em;color:var(--text-2)}
.reflection-list li{padding-left:3px;font-size:14.5px}
/* 历史图片画廊（含版权署名） */
.hist-imgs{display:grid;grid-template-columns:repeat(auto-fill,minmax(210px,1fr));gap:12px;margin-top:16px}
.hist-img{margin:0;border:1px solid var(--line-soft);border-radius:12px;overflow:hidden;background:#fff}
.hist-img img{width:100%;height:auto;display:block;background:#eef2f7}
.hist-img figcaption{padding:9px 12px;border-top:1px solid var(--line-soft)}
.hist-img figcaption strong{display:block;font-size:13.5px;color:var(--text-2)}
.hist-img figcaption .meta{display:block;margin-top:2px;font-size:11.5px;color:var(--accent-strong);line-height:1.4}
.hist-img figcaption .credit{display:block;margin-top:2px;font-size:11px;color:var(--muted);line-height:1.4}

/* 进阶概念：导航项 + 折叠卡片 */
.nav-item.adv{margin-top:8px;border-top:1px solid var(--line-soft);border-radius:0 0 10px 10px;color:var(--accent-strong)}
.nav-item.adv .nav-num{color:var(--accent-strong)}
.nav-item.adv.active{background:var(--accent-soft)}
.adv-item{border:1px solid var(--line-soft);border-radius:12px;background:var(--card);margin-bottom:10px;overflow:hidden}
.adv-item summary{padding:14px 18px;font-size:15.5px;font-weight:700;color:var(--text);cursor:pointer;list-style:none;display:flex;justify-content:space-between;align-items:center}
.adv-item summary::after{content:"＋";color:var(--accent);font-weight:600;font-size:16px}
.adv-item[open] summary::after{content:"－"}
.adv-item summary:hover{background:var(--accent-soft)}
.adv-body{padding:4px 18px 16px;color:var(--text-2);font-size:14.5px;line-height:1.7}
.adv-body p{margin-bottom:10px}
.adv-body p:last-child{margin-bottom:0}
.term-note{color:var(--muted);font-size:.94em;font-weight:400}

/* ---------- 实验 ---------- */
.demo-host{margin-top:20px}
.demo-section-head{display:flex;align-items:end;justify-content:space-between;gap:18px;margin:28px 2px 12px}
.demo-section-head h3{font-size:20px;letter-spacing:-.025em}
.demo-section-head p{color:var(--muted);font-size:13px}
.demo{position:relative;margin-bottom:16px;padding:23px 24px 25px;border:1px solid #dce5f2;border-radius:var(--radius-lg);background:linear-gradient(180deg,#fff,#fbfdff);box-shadow:var(--shadow-sm)}
.demo::before{content:"";position:absolute;left:0;right:0;top:0;height:3px;border-radius:var(--radius-lg) var(--radius-lg) 0 0;background:linear-gradient(90deg,var(--accent),var(--teal))}
.demo-title{display:flex;align-items:center;gap:9px;margin-bottom:8px;color:var(--accent-strong);font-size:15px;font-weight:740}
.demo-title span:last-child{display:flex;align-items:center;gap:8px}
.demo-title span:last-child::before{content:"LAB";padding:2px 6px;border-radius:5px;background:var(--accent-soft);color:var(--accent);font-size:9px;letter-spacing:.08em}
.demo h3{display:none}
.caption{margin:7px 0 13px;color:var(--muted);font-size:13.5px;line-height:1.65}
.demo-empty{padding:18px 20px;border:1px dashed #cfd9e6;border-radius:14px;background:rgba(255,255,255,.58);color:var(--muted);font-size:14px}
.controls{display:flex;flex-wrap:wrap;gap:12px 14px;align-items:center;margin:15px 0}
.controls label{display:flex;align-items:center;gap:8px;min-height:38px;padding:7px 10px;border:1px solid var(--line-soft);border-radius:10px;background:#fff;color:var(--text-2);font-size:13px}
/* 压缩实验：四个调节框 2×2 等宽网格，滑块轨道宽度一致 */
#ch-comp .controls{display:grid;grid-template-columns:1fr 1fr;gap:10px 14px;align-items:center}
#ch-comp .controls label{width:auto;min-width:0}
#ch-comp .controls input[type=range]{flex:0 0 150px;width:150px}
select{min-height:30px;border:1px solid var(--line);border-radius:8px;background:#fff;color:var(--text);padding:4px 30px 4px 9px;outline:none}
select:focus-visible{border-color:var(--accent);box-shadow:0 0 0 3px rgba(53,110,230,.13)}
input[type=range]{width:132px;height:4px;accent-color:var(--accent);cursor:pointer}
.controls span{min-width:48px;color:var(--accent-strong);font-size:12px;font-weight:670;font-variant-numeric:tabular-nums}
.play-btn,.upload-btn,.presets button{
  display:inline-flex;align-items:center;justify-content:center;min-height:38px;border-radius:999px;cursor:pointer;font-weight:650;
  transition:transform .14s ease,background .14s ease,border-color .14s ease,box-shadow .14s ease;
}
.play-btn{padding:0 16px;border:0;background:var(--accent);color:#fff;font-size:13px;box-shadow:0 7px 16px rgba(53,110,230,.19)}
.play-btn:hover{background:var(--accent-strong);transform:translateY(-1px)}
.play-btn.playing{background:#263247}
.play-btn svg{width:15px;height:15px;fill:currentColor}
.play-btn.icon-only{width:44px;height:44px;padding:0;border-radius:50%}
.play-btn.icon-only .play-tri{margin-left:2px}
.upload-row{display:flex;align-items:center;gap:11px;flex-wrap:wrap;margin:12px 0}
.upload-btn{gap:7px;min-height:38px;padding:0 14px;border:1px solid #bad0ef;background:#fff;color:var(--accent-strong);font-size:13px}
.upload-btn:hover{background:var(--accent-soft);border-color:#91b4e6}
.upload-btn svg{width:15px;height:15px}
.upload-name{max-width:100%;overflow:hidden;text-overflow:ellipsis;white-space:nowrap;color:var(--muted);font-size:12.5px}
.scope,.eq-svg{display:block;width:100%;max-width:100%;margin:13px 0;border:1px solid var(--line-soft);border-radius:13px;background:#fff}
.scope{height:120px}
.eq-svg{height:200px;touch-action:none}
.eq-svg .eq-node,.eq-svg .adsr-h{cursor:grab;transform-box:fill-box;transform-origin:center;transition:transform .12s ease}
.eq-svg .eq-node:hover,.eq-svg .adsr-h:hover{transform:scale(1.3)}
.eq-svg.is-dragging .eq-node,.eq-svg.is-dragging .adsr-h{cursor:grabbing}
.adsr-values{display:flex;flex-wrap:wrap;gap:7px;margin:-4px 0 10px}
.adsr-values span{padding:4px 8px;border-radius:999px;background:var(--card-soft);color:var(--muted);font-size:11.5px;font-variant-numeric:tabular-nums}
.mini-label{margin:16px 0 5px;color:var(--muted);font-size:12px;font-weight:650}
.param-hints{margin:6px 0 0;display:grid;gap:6px}
.param-hint{font-size:13px;color:var(--text-2);line-height:1.6;margin:0}
.param-hint::before{content:"· ";color:var(--accent)}
.param-hint strong{color:var(--text);font-weight:650}

/* 压缩实验：上传行带操作按钮 + 单图视图切换 */
.upload-row .upload-name{flex:1 1 auto;min-width:70px;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.upload-actions{display:flex;align-items:center;gap:8px;margin-left:auto}
.ab-btn{padding:7px 14px;border:1px solid var(--line);border-radius:8px;background:var(--card-soft);color:var(--text-2);font-size:13px;cursor:pointer}
.ab-btn.off{opacity:.6}
.graph-stage{position:relative}
.graph-switch{position:absolute;right:10px;bottom:10px;z-index:2;padding:5px 12px;font-size:11.5px;border:1px solid var(--line);border-radius:8px;background:rgba(255,255,255,.88);color:var(--text-2);cursor:pointer;box-shadow:var(--shadow-sm)}
.graph-switch:hover{border-color:var(--accent);color:var(--accent-strong)}
.play-btn:disabled{opacity:.35;cursor:not-allowed;box-shadow:none}
.play-btn:disabled:hover{background:var(--accent)}
.signal-chain{display:flex;align-items:center;justify-content:center;gap:7px;flex-wrap:wrap;margin:13px 0;padding:13px 14px;border:1px solid #dce8f8;border-radius:12px;background:var(--accent-soft);font-family:ui-monospace,SFMono-Regular,Menlo,monospace;color:var(--text-2);font-size:12.5px}
.signal-chain .arrow{color:var(--accent);font-weight:760}
.signal-chain .node{padding:3px 8px;border-radius:7px}
.signal-chain .node.on{background:var(--accent);color:#fff}
.harmonics{display:flex;flex-direction:column;align-items:stretch;gap:6px}
.harm-row{display:grid;grid-template-columns:58px minmax(120px,240px) 36px;align-items:center;gap:10px;color:var(--text-2);font-size:13px}
.harm-row input{width:100%}
.harm-row .hv{min-width:30px;color:var(--accent-strong);font-size:12px}
.presets{display:flex;gap:8px;flex-wrap:wrap;margin-top:12px}
.presets button{min-height:34px;padding:0 13px;border:1px solid var(--line);background:#fff;color:var(--text-2);font-size:12.5px}
.presets button:hover{border-color:#9cb9e4;background:var(--accent-soft);color:var(--accent-strong)}
.keyboard{display:flex;justify-content:center;gap:3px;flex-wrap:wrap;margin:16px 0}
.keyboard.left{justify-content:flex-start}
.key{display:flex;width:48px;height:76px;align-items:flex-end;justify-content:center;padding:0 4px 7px;border:1px solid var(--line);border-radius:7px;background:#fff;color:var(--muted);font-size:10px;cursor:pointer;user-select:none;transition:background .1s ease,transform .1s ease}
.key:hover{background:var(--accent-soft);color:var(--accent-strong)}
.key:active{transform:translateY(2px)}
.pitch-out{margin:12px 0;padding:22px;border:1px solid var(--line-soft);border-radius:13px;background:#fff;text-align:center;color:var(--text-2);font-size:15px}
.pitch-out b{color:var(--accent-strong);font-size:21px}
.gr-meter{margin:14px 0;padding:12px 14px;border:1px solid var(--line-soft);border-radius:12px;background:#fff}
.gr-meter>span{display:block;margin-bottom:7px;color:var(--muted);font-size:12px}
.gr-bar{height:9px;overflow:hidden;border-radius:999px;background:#edf1f5}
.gr-bar>div{height:100%;width:0;border-radius:inherit;background:linear-gradient(90deg,var(--success),var(--warn));transition:width .08s linear}

/* ---------- 章节底部 ---------- */
.chapter-footer{display:flex;align-items:center;justify-content:space-between;gap:12px;margin-top:24px;padding-top:22px;border-top:1px solid var(--line)}
.chapter-nav-btn{display:flex;align-items:center;justify-content:center;width:48px;height:48px;border-radius:50%;border:1px solid var(--line);background:var(--card-soft);color:var(--accent-strong);cursor:pointer;transition:background .14s ease,border-color .14s ease,transform .14s ease}
.chapter-nav-btn:hover{background:var(--accent-soft);border-color:#9cb9e4;transform:translateY(-1px)}
.chapter-nav-btn:disabled{opacity:.35;cursor:not-allowed;transform:none}
.chapter-nav-btn:disabled:hover{background:var(--card-soft);border-color:var(--line)}
.chapter-nav-btn svg{width:20px;height:20px;fill:none;stroke:currentColor;stroke-width:2;stroke-linecap:round;stroke-linejoin:round}

.menu-btn{display:none;position:fixed;left:14px;top:14px;z-index:120;width:42px;height:42px;align-items:center;justify-content:center;border:1px solid rgba(210,220,233,.9);border-radius:12px;background:rgba(255,255,255,.88);box-shadow:var(--shadow-md);backdrop-filter:blur(12px);cursor:pointer}
.nav-backdrop{position:fixed;inset:0;z-index:90;background:rgba(16,27,45,.35);backdrop-filter:blur(2px)}

footer{border-top:1px solid var(--line);background:rgba(255,255,255,.50)}
.footer-inner{max-width:1160px;margin:0 auto;padding:30px 24px 40px;text-align:center;color:var(--muted);font-size:12.5px}
.footer-inner strong{color:var(--text-2)}

/* ---------- 可访问性 ---------- */
button:focus-visible,input:focus-visible,select:focus-visible,.key:focus-visible{outline:3px solid rgba(53,110,230,.23);outline-offset:2px}
@media (prefers-reduced-motion:reduce){
  *,*::before,*::after{scroll-behavior:auto!important;animation-duration:.01ms!important;animation-iteration-count:1!important;transition-duration:.01ms!important}
}

/* ---------- 平板与手机 ---------- */
@media(max-width:980px){
  .layout{display:block;max-width:850px;padding:28px 18px 66px}
  .menu-btn{display:flex}
  .sidebar{position:fixed;z-index:100;left:0;top:0;width:min(88vw,320px);height:100dvh;max-height:none;border-radius:0 20px 20px 0;transform:translateX(-105%);transition:transform .25s ease;box-shadow:var(--shadow-lg)}
  body.nav-open{overflow:hidden}
  body.nav-open .sidebar{transform:none}
  .sidebar-close{display:flex}
  .hero{padding-top:70px}
}

@media(max-width:640px){
  body{font-size:15px}
  .hero{padding:64px 18px 38px}
  .brand-mark{width:70px;height:70px;margin-bottom:18px}
  .hero h1{font-size:35px}
  .layout{padding:22px 13px 54px}
  .block,.block.intro,.demo{padding:20px 18px;border-radius:17px}
  .block.intro .one-line{font-size:16.5px}
  .block p{font-size:14.5px}
  .controls{align-items:stretch}
  .controls label{width:100%;justify-content:space-between;flex-wrap:wrap}
  .controls label input[type=range]{flex:1;min-width:130px}
  .play-btn:not(.icon-only){width:100%}
  .upload-name{width:100%}
  .harm-row{grid-template-columns:52px minmax(110px,1fr) 32px}
  .chapter-footer{grid-template-columns:1fr 1fr}
  }
@media(max-width:980px){
  body.nav-open .menu-btn{opacity:0;pointer-events:none}
}