/* 小学数学「比的认识」实验课件 · 公共样式（纸张风格，克制配色） */
:root{
  --ink:#17324d; --ink-soft:#4b6177; --paper:#fffdf8; --bg:#fbf3e4;
  --coral:#c84833; --coral-soft:#f6d9cf; --teal:#28768d; --teal-soft:#d6ebee;
  --leaf:#4f7f3a; --leaf-soft:#e1efd8; --mustard:#f2c94c; --mustard-soft:#fdf1c7;
  --line:rgba(23,50,77,.16); --shadow:6px 6px 0 var(--ink);
}
*{box-sizing:border-box}
html,body{margin:0}
body{
  font-family:"PingFang SC","Hiragino Sans GB","Noto Sans SC","Microsoft YaHei",system-ui,sans-serif;
  color:var(--ink); background:var(--bg); line-height:1.6; font-size:18px;
  background-image:linear-gradient(var(--line) 1px,transparent 1px),linear-gradient(90deg,var(--line) 1px,transparent 1px);
  background-size:28px 28px; background-position:-1px -1px;
}
body::before{content:"";position:fixed;inset:0;background:rgba(251,243,228,.72);z-index:-1}
button,input{font-family:inherit}
.page-shell{max-width:1180px;margin:0 auto;padding:22px 22px 60px}

/* 课程导航 */
.course-nav{display:grid;grid-template-columns:repeat(4,1fr);gap:14px;margin-bottom:26px}
.course-nav a{display:flex;align-items:center;gap:12px;padding:12px 16px;border:2px solid var(--ink);border-radius:12px;
  background:var(--paper);color:var(--ink);text-decoration:none;box-shadow:3px 3px 0 var(--ink);transition:transform .15s}
.course-nav a:hover{transform:translate(-1px,-1px)}
.course-nav b{font-size:22px;font-weight:800;font-variant-numeric:tabular-nums}
.course-nav span{display:flex;flex-direction:column;font-weight:700;line-height:1.25}
.course-nav small{font-weight:500;color:var(--ink-soft);font-size:13px}
.course-nav a[aria-current=page]{background:var(--ink);color:#fff}
.course-nav a[aria-current=page] small{color:#c9d6e2}
@media(max-width:820px){.course-nav{grid-template-columns:repeat(2,1fr)}}

/* 顶部 */
.intro{display:grid;grid-template-columns:1fr 300px;gap:28px;align-items:start;margin-bottom:26px}
@media(max-width:900px){.intro{grid-template-columns:1fr}}
.eyebrow{margin:0 0 6px;color:var(--teal);font-weight:800;letter-spacing:2px;font-size:14px}
h1{font-size:44px;line-height:1.2;margin:0 0 12px;font-weight:900}
h1 mark{background:linear-gradient(transparent 58%,var(--mustard) 58%);color:inherit;padding:0 2px}
.lead{color:var(--ink-soft);margin:0;font-size:19px}
.guess{position:relative;background:var(--mustard);border-radius:4px;padding:22px 20px 16px;transform:rotate(2deg);box-shadow:4px 6px 0 rgba(23,50,77,.25)}
.guess::before{content:"";position:absolute;top:-12px;left:50%;width:90px;height:24px;transform:translateX(-50%) rotate(-3deg);background:rgba(255,255,255,.6)}
.guess b{display:block;font-size:20px;margin-bottom:6px}
.guess p{margin:0 0 10px;font-weight:600}
.guess .chips{display:flex;gap:8px;flex-wrap:wrap}
.guess .chips button{border:2px solid var(--ink);background:#fff8de;border-radius:999px;padding:4px 14px;font-weight:700;cursor:pointer}
.guess .chips button[aria-pressed=true]{background:var(--ink);color:#fff}
.guess small{display:block;margin-top:8px;font-weight:600;color:#6b5512}

/* 实验卡 */
.experiment{background:var(--paper);border:2px solid var(--ink);border-radius:16px;box-shadow:var(--shadow);margin-bottom:30px;overflow:hidden}
.ex-head{display:flex;justify-content:space-between;align-items:flex-end;gap:16px;padding:20px 26px;border-bottom:1.5px dashed var(--line)}
.ex-head h2{margin:0;font-size:28px}
.pill{border:2px solid var(--ink);border-radius:999px;padding:4px 14px;font-weight:800;font-size:15px;white-space:nowrap;background:var(--mustard-soft)}
.workspace{display:grid;grid-template-columns:240px 1fr;gap:0}
@media(max-width:900px){.workspace{grid-template-columns:1fr}}
.desk{padding:20px;border-right:1.5px dashed var(--line);background:#fffaf0;display:flex;flex-direction:column;gap:12px}
@media(max-width:900px){.desk{border-right:none;border-bottom:1.5px dashed var(--line)}}
.desk h3{margin:0;font-size:18px}
.desk .hint{margin:0;font-size:14px;color:var(--ink-soft)}
.display{padding:18px 22px;min-width:0}

.btn{display:inline-flex;align-items:center;justify-content:center;gap:6px;border:2px solid var(--ink);background:#fff;color:var(--ink);
  border-radius:10px;padding:10px 14px;font-size:17px;font-weight:800;cursor:pointer;box-shadow:3px 3px 0 var(--ink);transition:transform .08s,box-shadow .08s}
.btn:active{transform:translate(2px,2px);box-shadow:1px 1px 0 var(--ink)}
.btn.primary{background:var(--ink);color:#fff}
.btn[disabled]{opacity:.4;pointer-events:none}
.choices{display:flex;flex-wrap:wrap;gap:8px}
.choices button{min-width:46px;border:2px solid var(--ink);background:#fff;border-radius:8px;padding:6px 10px;font-weight:800;font-size:16px;cursor:pointer}
.choices button[aria-pressed=true]{background:var(--ink);color:#fff}
.range-label{display:flex;justify-content:space-between;font-weight:700;font-size:15px}
.range-label output{color:var(--teal);font-variant-numeric:tabular-nums}
input[type=range]{width:100%;accent-color:var(--teal);height:28px;cursor:pointer}

.legend{display:flex;flex-wrap:wrap;gap:16px;font-size:14px;color:var(--ink-soft);margin-bottom:6px;align-items:center}
.legend i{display:inline-block;width:22px;height:5px;border-radius:3px;vertical-align:middle;margin-right:6px}
.stage{width:100%;height:auto;display:block}
.status{margin:10px 0 0;padding:10px 14px;border-radius:10px;background:var(--teal-soft);font-weight:700;min-height:46px}
.invariant{display:flex;justify-content:space-between;align-items:center;gap:12px;margin-top:12px;padding:10px 16px;border-radius:10px;background:var(--leaf-soft);color:#2e5a1f;font-weight:700}
.invariant b{font-size:20px}
.invariant.broken{background:var(--coral-soft);color:#8b2b1c}

/* 数字身份：实际的量 / 比值 */
.q{display:inline-block;border:1.5px solid var(--teal);color:var(--teal);border-radius:6px;padding:0 6px;font-weight:800;background:#fff;white-space:nowrap}
.v{display:inline-block;background:var(--ink);color:#fff;border-radius:999px;padding:0 10px;font-weight:800;white-space:nowrap}

/* 思考条 / 结论 */
.thinking{display:grid;grid-template-columns:120px 1fr;gap:18px;align-items:center;background:var(--ink);color:#fff;border-radius:16px;padding:20px 26px;margin-bottom:26px}
.thinking>b{font-size:15px;letter-spacing:2px;color:var(--mustard)}
.thinking h2{margin:0 0 4px;font-size:26px}
.thinking p{margin:0;color:#d5e0ea}
@media(max-width:700px){.thinking{grid-template-columns:1fr}}
.meter{display:grid;grid-template-columns:120px 1fr 80px;gap:12px;align-items:center;margin-top:8px}
.meter .track{height:14px;border-radius:999px;background:rgba(255,255,255,.18);overflow:hidden}
.meter .track span{display:block;height:100%;background:var(--mustard);transition:width .5s}

details.answer{background:var(--paper);border:2px solid var(--ink);border-radius:16px;margin-bottom:26px;box-shadow:var(--shadow)}
details.answer summary{list-style:none;cursor:pointer;display:flex;justify-content:space-between;align-items:center;padding:18px 24px}
details.answer summary::-webkit-details-marker{display:none}
details.answer summary small{display:block;color:var(--teal);font-weight:800;letter-spacing:2px;font-size:13px}
details.answer summary b{font-size:22px}
details.answer summary .plus{font-size:28px;font-weight:900;transition:transform .2s}
details.answer[open] summary .plus{transform:rotate(45deg)}
.answer-body{padding:0 24px 22px;border-top:1.5px dashed var(--line)}
.formula{font-size:30px;font-weight:900;text-align:center;margin:16px 0;padding:14px;border-radius:12px;background:var(--mustard-soft)}
.grid2{display:grid;grid-template-columns:1fr 1fr;gap:14px}
@media(max-width:760px){.grid2{grid-template-columns:1fr}}
.grid2 article{border:1.5px solid var(--line);border-radius:12px;padding:12px 16px;background:#fff}
.grid2 article b{display:block;font-size:20px;margin:2px 0}
.mistakes{margin:8px 0 0;padding-left:22px}
.mistakes li{margin:6px 0}
.mistakes s{color:var(--coral)}

.challenge{background:var(--paper);border:2px solid var(--ink);border-radius:16px;padding:20px 24px;box-shadow:var(--shadow);margin-bottom:26px}
.challenge h2{margin:4px 0 6px;font-size:26px}

footer{display:flex;justify-content:space-between;color:var(--ink-soft);font-size:14px;padding-top:8px;border-top:1.5px dashed var(--line)}
.sound-toggle{position:fixed;right:18px;bottom:18px;z-index:20;border:2px solid var(--ink);background:var(--paper);border-radius:999px;padding:6px 14px;font-weight:800;cursor:pointer;box-shadow:3px 3px 0 var(--ink)}
.frac{display:inline-flex;flex-direction:column;align-items:center;vertical-align:middle;line-height:1.05;font-size:.85em;margin:0 .1em}
.frac>span:first-child{border-bottom:.08em solid currentColor;padding:0 .12em}
@media(max-width:700px){h1{font-size:32px}body{font-size:17px}}