/* ===== 物理公式动画馆 · 全站样式 ===== */
:root{
  --bg:#f4f6fa; --card:#ffffff; --ink:#1c2733; --muted:#5b6b7b;
  --blue:#2563eb; --green:#059669; --orange:#ea580c; --purple:#7c3aed;
  --red:#dc2626; --teal:#0d9488; --pink:#db2777;
  --line:#e2e8f0; --shadow:0 2px 12px rgba(16,38,64,.08);
  --radius:14px;
  --mono:ui-monospace,Consolas,"Courier New",monospace;
  --serif:"Times New Roman",Georgia,"STIX Two Text",serif;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;font-family:"PingFang SC","Microsoft YaHei",system-ui,sans-serif;background:var(--bg);color:var(--ink);line-height:1.7}
a{color:var(--blue)}
img,canvas{max-width:100%}

/* ---- 顶部导航 ---- */
.nav{position:sticky;top:0;z-index:60;background:rgba(255,255,255,.94);backdrop-filter:blur(10px);border-bottom:1px solid var(--line)}
.nav-in{max-width:1080px;margin:auto;display:flex;align-items:center;gap:12px;padding:10px 18px}
.brand{font-weight:800;font-size:1.05rem;color:var(--ink);text-decoration:none;white-space:nowrap}
.brand span{color:var(--blue)}
.links{display:flex;gap:2px;overflow-x:auto;scrollbar-width:none;-ms-overflow-style:none}
.links::-webkit-scrollbar{display:none}
.links a{padding:6px 11px;border-radius:999px;color:var(--muted);text-decoration:none;white-space:nowrap;font-size:.88rem}
.links a:hover{background:#eef2ff;color:var(--blue)}
.links a.here{background:#e5edff;color:var(--blue);font-weight:700}

.wrap{max-width:1080px;margin:auto;padding:18px}

/* ---- 首页 hero ---- */
.hero{background:linear-gradient(135deg,#1d4ed8 0%,#7c3aed 55%,#db2777 110%);color:#fff;border-radius:22px;padding:46px 34px;margin-top:20px;box-shadow:var(--shadow);position:relative;overflow:hidden}
.hero::after{content:"";position:absolute;inset:0;background:radial-gradient(circle at 85% 20%,rgba(255,255,255,.18),transparent 40%),radial-gradient(circle at 15% 90%,rgba(255,255,255,.12),transparent 45%)}
.hero h1{margin:0 0 10px;font-size:2.1rem;letter-spacing:1px}
.hero p{margin:0;opacity:.93;max-width:640px}
.stats{display:flex;gap:14px;margin-top:22px;flex-wrap:wrap;position:relative;z-index:1}
.stat{background:rgba(255,255,255,.16);border:1px solid rgba(255,255,255,.35);border-radius:14px;padding:10px 20px;text-align:center}
.stat b{display:block;font-size:1.7rem;font-family:var(--mono)}
.stat i{font-style:normal;font-size:.82rem;opacity:.9}

.sec-h{display:flex;align-items:center;gap:10px;margin:34px 0 14px;font-size:1.25rem}
.sec-h .bar{width:6px;height:24px;border-radius:3px;background:linear-gradient(#2563eb,#7c3aed)}

/* ---- 卡片栅格（首页） ---- */
.grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(310px,1fr));gap:16px}
.gcard{background:var(--card);border-radius:var(--radius);box-shadow:var(--shadow);padding:20px;text-decoration:none;color:var(--ink);display:block;border-top:4px solid var(--blue);transition:transform .15s,box-shadow .15s}
.gcard:hover{transform:translateY(-3px);box-shadow:0 8px 22px rgba(16,38,64,.13)}
.gcard h3{margin:0 0 6px;font-size:1.06rem}
.gcard p{margin:0 0 10px;color:var(--muted);font-size:.9rem}
.gcard .mini{font-family:var(--serif);font-style:italic;font-size:1.02rem;color:#334;background:#f6f8ff;border-radius:8px;padding:6px 10px;line-height:2}
.t-blue{border-top-color:var(--blue)} .t-green{border-top-color:var(--green)} .t-orange{border-top-color:var(--orange)} .t-purple{border-top-color:var(--purple)} .t-teal{border-top-color:var(--teal)} .t-pink{border-top-color:var(--pink)}

/* ---- 公式卡片（内容页） ---- */
.page-head{margin:22px 0 6px}
.page-head h1{font-size:1.65rem;margin:0}
.page-head .sub{color:var(--muted)}
.card{background:var(--card);border-radius:var(--radius);box-shadow:var(--shadow);padding:22px;margin:20px 0;scroll-margin-top:70px}
.card-head{display:flex;justify-content:space-between;align-items:flex-start;gap:10px;flex-wrap:wrap;margin-bottom:12px}
.card-head h2{margin:0;font-size:1.28rem}
.card-head small{color:var(--muted);font-weight:400;margin-left:8px}
.badge{padding:3px 12px;border-radius:999px;font-size:.78rem;font-weight:600;color:#fff;flex-shrink:0}
.b-mech{background:var(--green)} .b-elec{background:var(--orange)} .b-heat{background:var(--red)}
.b-motion{background:var(--blue)} .b-em{background:var(--purple)} .b-astro{background:var(--teal)}

.demo{width:100%;height:290px;display:block;background:#fdfefe;border:1px solid var(--line);border-radius:12px}

.controls{display:flex;flex-wrap:wrap;gap:10px 22px;margin:14px 0 4px}
.controls label{display:flex;align-items:center;gap:8px;font-size:.92rem;color:#334155}
.controls input[type=range]{width:150px;accent-color:var(--blue)}
.controls b{font-family:var(--mono);min-width:64px;font-weight:600;color:var(--blue)}
select.btn{padding:5px 10px}

.btns{display:flex;gap:10px;flex-wrap:wrap;margin-top:10px}
.btn{border:1px solid #cfdaf3;background:#eef3ff;color:#1e40af;padding:7px 16px;border-radius:10px;font-size:.92rem;cursor:pointer;transition:.15s;font-family:inherit}
.btn:hover{background:#dbe6ff}
.btn.ghost{background:#fff;color:#475569;border-color:#d7dee8}
.btn.ghost:hover{background:#f1f5f9}
.readout{display:flex;gap:8px;flex-wrap:wrap;margin-top:12px}
.chip{background:#f0f6ff;border:1px solid #dbe7ff;border-radius:999px;padding:2px 13px;font-size:.88rem;color:#334155}
.chip b{font-family:var(--mono);color:var(--blue)}

h3.sub-t{margin:26px 0 8px;font-size:1.05rem;color:#0f172a;border-left:4px solid var(--purple);padding-left:10px}

/* ---- 数学公式排版 ---- */
.fx{font-family:var(--serif);font-style:italic;font-size:1.42rem;text-align:center;background:#fafbff;border:1.5px dashed #c7d5f2;border-radius:12px;padding:16px 12px;margin:12px 0;line-height:2.15;overflow-x:auto}
.fx.big{font-size:1.7rem}
.frac{display:inline-flex;flex-direction:column;text-align:center;vertical-align:-0.62em;margin:0 .18em;line-height:1.25}
.frac .fn{border-bottom:1.6px solid currentColor;padding:0 .28em}
.frac .fd{padding:0 .28em}
.sqrt{white-space:nowrap}
.sqrt .rad{border-top:1.5px solid currentColor;padding:0 .15em;margin-left:-2px}
.vars{display:grid;grid-template-columns:auto 1fr;gap:5px 16px;max-width:560px;margin:8px auto;font-size:.95rem}
.vars .k{font-family:var(--serif);font-style:italic;font-size:1.08em;text-align:right;color:#0f172a}
.vars .d{color:var(--muted)}
.note{background:#fffbeb;border:1px solid #fde68a;border-radius:10px;padding:8px 14px;font-size:.9rem;color:#92400e;margin:10px 0}
.tip{background:#ecfdf5;border:1px solid #a7f3d0;border-radius:10px;padding:8px 14px;font-size:.9rem;color:#065f46;margin:10px 0}

/* ---- 变形 tabs ---- */
.tabs{display:flex;gap:8px;flex-wrap:wrap;margin:10px 0}
.tabs button{border:1.5px solid #cdd9ee;background:#fff;color:#334155;padding:6px 16px;border-radius:999px;cursor:pointer;font-size:.9rem;font-family:inherit;transition:.15s}
.tabs button.active{background:var(--blue);border-color:var(--blue);color:#fff}
.panel{display:none;background:#f8faff;border-left:4px solid var(--blue);border-radius:0 10px 10px 0;padding:12px 16px;margin-bottom:8px;font-size:.96rem}
.panel.active{display:block;animation:fadeUp .3s ease}
.panel .fx{margin:8px 0;font-size:1.3rem;background:#fff}

/* ---- 推导分步 ---- */
.steps .step{display:none;background:#f5f3ff;border-left:4px solid var(--purple);border-radius:0 10px 10px 0;padding:14px 18px;margin-bottom:8px}
.steps .step.active{display:block;animation:fadeUp .35s ease}
.step h4{margin:0 0 8px;color:var(--purple);font-size:1rem}
.step .fx{background:#fff}
.step-nav{display:flex;align-items:center;gap:12px;margin-top:6px}
.step-nav button{width:auto}
.step-ct{font-family:var(--mono);color:var(--muted);font-size:.9rem}

.pager{display:flex;justify-content:space-between;gap:10px;margin:30px 0 10px;flex-wrap:wrap}
.pager a{text-decoration:none;background:#fff;border:1px solid var(--line);border-radius:12px;padding:10px 18px;color:var(--blue);font-weight:600;box-shadow:var(--shadow)}
footer.ft{text-align:center;color:var(--muted);font-size:.85rem;padding:26px 0 34px}

@keyframes fadeUp{from{opacity:0;transform:translateY(7px)}to{opacity:1;transform:none}}
@media (max-width:640px){.hero{padding:32px 22px}.hero h1{font-size:1.55rem}.demo{height:250px}.fx{font-size:1.2rem}}