/* How to AI Almost Anything · 交互课共享样式 v4（现代 AI 产品风：靛紫渐变 + 纯净白 + 柔和阴影 + 大圆角） */
:root{
  --bg:#f5f6fb; --bg2:#eef0f9; --surface:#ffffff;
  --ink:#16142b; --ink2:#5a5670; --muted:#9591a8; --faint:#bdb9cc;
  --indigo:#6366f1; --violet:#8b5cf6; --indigo-d:#4f46e5;
  --grad:linear-gradient(135deg,#6366f1,#8b5cf6);
  --grad-soft:linear-gradient(135deg,#eef0fe,#f3eefe);
  --indigo-50:#eef0fe; --violet-50:#f5f0fe;
  --amber:#f59e0b; --amber-50:#fef5e7; --amber-d:#b45309;
  --green:#10b981; --green-50:#e7f7f1; --green-d:#047857;
  --rose:#f43f5e; --rose-50:#fdeef0;
  --line:#e9eaf3; --line2:#dcdcec;
  --sh-sm:0 1px 3px rgba(22,20,43,.05),0 1px 2px rgba(22,20,43,.04);
  --sh-md:0 4px 18px rgba(22,20,43,.07);
  --sh-lg:0 16px 40px rgba(99,102,241,.13);
  --sh-glow:0 10px 30px rgba(99,102,241,.28);
  --sans:-apple-system,"Segoe UI","PingFang SC","Microsoft YaHei",system-ui,sans-serif;
  --mono:"SF Mono","Cascadia Mono",Consolas,monospace;
  --maxw:680px;
}
*{box-sizing:border-box;margin:0;padding:0}
html,body{height:100%}
body{background:var(--bg);color:var(--ink2);font-family:var(--sans);line-height:1.8;
  -webkit-font-smoothing:antialiased;text-rendering:optimizeLegibility;
  display:flex;flex-direction:column;min-height:100vh;font-size:16.5px;position:relative;overflow-x:hidden}
body::before{content:"";position:fixed;top:-200px;right:-160px;width:520px;height:520px;border-radius:50%;
  background:radial-gradient(circle,rgba(139,92,246,.16),transparent 65%);filter:blur(20px);z-index:0;pointer-events:none}
body::after{content:"";position:fixed;bottom:-220px;left:-180px;width:560px;height:560px;border-radius:50%;
  background:radial-gradient(circle,rgba(99,102,241,.14),transparent 65%);filter:blur(20px);z-index:0;pointer-events:none}

.top{position:sticky;top:0;z-index:50;background:rgba(245,246,251,.82);backdrop-filter:blur(16px) saturate(1.4)}
.top-in{max-width:var(--maxw);margin:0 auto;padding:14px 24px 10px;display:flex;align-items:center;gap:18px}
.logo{display:flex;align-items:center;gap:9px;white-space:nowrap}
.logo .mk{width:24px;height:24px;border-radius:7px;background:var(--grad);box-shadow:var(--sh-glow);flex-shrink:0;display:flex;align-items:center;justify-content:center}
.logo .mk svg{display:block}
.logo .tt{font-size:14px;font-weight:750;color:var(--ink);letter-spacing:-.2px}
.dots{display:flex;gap:6px;flex:1;justify-content:center;flex-wrap:nowrap;overflow:hidden}
.dot{width:7px;height:7px;border-radius:50%;background:var(--line2);cursor:pointer;transition:.25s;padding:0;border:none;flex-shrink:0}
.dot.done{background:var(--violet);opacity:.5}
.dot.now{background:var(--indigo);transform:scale(1.6);box-shadow:0 0 0 4px rgba(99,102,241,.15)}
.step-count{font-size:12px;color:var(--muted);white-space:nowrap;font-family:var(--mono);font-weight:600}
.barwrap{max-width:var(--maxw);margin:0 auto;height:5px;background:var(--bg2);border-radius:999px;overflow:hidden}
.barfill{height:100%;background:var(--grad);width:0;transition:width .45s cubic-bezier(.4,0,.2,1);border-radius:999px}

.resume{max-width:var(--maxw);margin:0 auto;padding:0 24px;overflow:hidden;max-height:0;transition:max-height .4s,padding .4s;position:relative;z-index:2}
.resume.show{max-height:64px;padding:10px 24px 0}
.resume-in{display:flex;align-items:center;gap:12px;background:var(--violet-50);border:1px solid #e7ddfb;border-radius:13px;padding:10px 16px;font-size:13.5px;color:#6d4bb8}
.resume-in a{color:var(--indigo-d);cursor:pointer;font-weight:600;text-decoration:none}
.resume-in a:hover{text-decoration:underline}
.resume-in .x{margin-left:auto;cursor:pointer;color:var(--muted);font-size:19px;line-height:1}

.stage{flex:1;display:flex;align-items:flex-start;justify-content:center;padding:46px 24px 44px;position:relative;z-index:1}
.step{display:none;max-width:var(--maxw);width:100%}
.step.active{display:block;animation:rise .55s cubic-bezier(.16,1,.3,1)}
@keyframes rise{from{opacity:0;transform:translateY(20px)}to{opacity:1;transform:none}}
.all-mode .step{display:block;margin-bottom:60px;border:1px dashed var(--line2);border-radius:20px;padding:20px}
.all-mode .top,.all-mode .nav,.all-mode .resume{display:none}

.badge{display:inline-flex;align-items:center;gap:8px;font-size:12px;letter-spacing:.5px;font-weight:700;padding:6px 14px 6px 11px;border-radius:999px;margin-bottom:22px;background:var(--indigo-50);color:var(--indigo-d)}
.badge .bi{width:16px;height:16px;display:flex}
.badge.hook{background:var(--amber-50);color:var(--amber-d)}
.badge.sci{background:var(--violet-50);color:#7c3aed}
.badge.quiz{background:var(--green-50);color:var(--green-d)}

h1.big{font-size:clamp(36px,6.5vw,56px);line-height:1.08;letter-spacing:-1.5px;font-weight:820;color:var(--ink)}
.grad-txt{background:var(--grad);-webkit-background-clip:text;background-clip:text;-webkit-text-fill-color:transparent}
h2.q{font-size:clamp(26px,4.4vw,37px);line-height:1.24;font-weight:800;letter-spacing:-.8px;color:var(--ink);margin-bottom:18px}
.lead{font-size:18px;color:var(--ink2);margin:20px 0;line-height:1.7}
p{margin:15px 0;color:var(--ink2)}
.em{color:var(--indigo-d);font-weight:700}
.dim{color:var(--muted);font-size:14px}

.callout{display:flex;gap:15px;background:var(--surface);border-radius:16px;padding:18px 20px;margin:24px 0;box-shadow:var(--sh-sm);border:1px solid var(--line)}
.callout .ic{width:38px;height:38px;border-radius:11px;flex-shrink:0;display:flex;align-items:center;justify-content:center;background:var(--indigo-50)}
.callout.sci .ic{background:var(--violet-50)}
.callout .lbl{font-size:11.5px;letter-spacing:.8px;color:var(--indigo-d);text-transform:uppercase;font-weight:700;display:block;margin-bottom:4px}
.callout.sci .lbl{color:#7c3aed}
.callout .bd{font-size:15px;color:var(--ink);line-height:1.65}
.callout .bd b{color:var(--indigo-d)}.callout.sci .bd b{color:#7c3aed}

.vcard{background:var(--surface);border-radius:18px;overflow:hidden;margin:24px 0;box-shadow:var(--sh-md);border:1px solid var(--line);transition:.25s}
.vcard:hover{box-shadow:var(--sh-lg);transform:translateY(-2px)}
.vcard video{display:block;width:100%;max-height:54vh;background:#000}
.vplay{display:flex;align-items:center;gap:15px;padding:16px 18px;cursor:pointer;transition:.18s}
.vplay:hover{background:var(--indigo-50)}
.vplay .pb{width:46px;height:46px;border-radius:14px;background:var(--grad);flex-shrink:0;box-shadow:var(--sh-glow);display:flex;align-items:center;justify-content:center;transition:.2s}
.vplay:hover .pb{transform:scale(1.07) rotate(-3deg)}
.vplay .tx{font-size:15px;color:var(--ink);font-weight:700}
.vplay .tx s{display:block;font-weight:500;color:var(--muted);font-size:12.5px;text-decoration:none;margin-top:1px}
.vplay .tm{margin-left:auto;font-size:12.5px;color:var(--indigo-d);font-family:var(--mono);font-weight:600;background:var(--indigo-50);padding:4px 10px;border-radius:8px}
.vstage{display:none}.vstage.on{display:block}
.speedbar{display:flex;gap:6px;padding:11px 16px;background:var(--bg2);align-items:center;flex-wrap:wrap}
.speedbar .sl{font-size:11.5px;color:var(--muted);margin-right:4px;font-weight:700;letter-spacing:.5px}
.spd{background:var(--surface);border:1px solid var(--line2);color:var(--ink2);padding:5px 13px;border-radius:9px;cursor:pointer;font-size:12.5px;font-family:inherit;font-weight:700;transition:.15s}
.spd:hover{border-color:var(--indigo);color:var(--indigo-d)}
.spd.on{background:var(--grad);color:#fff;border-color:transparent;box-shadow:0 2px 8px rgba(99,102,241,.3)}

ul.steps{list-style:none;margin:22px 0;display:flex;flex-direction:column;gap:10px}
ul.steps li{padding:15px 18px 15px 56px;position:relative;background:var(--surface);border-radius:14px;font-size:15.5px;color:var(--ink);box-shadow:var(--sh-sm);border:1px solid var(--line);line-height:1.55}
ul.steps li:before{content:attr(data-n);position:absolute;left:14px;top:50%;transform:translateY(-50%);width:30px;height:30px;border-radius:9px;background:var(--grad-soft);color:var(--indigo-d);font-size:13px;font-weight:800;font-family:var(--mono);display:flex;align-items:center;justify-content:center}
ul.steps li b{color:var(--indigo-d)}

.flow{display:flex;align-items:stretch;gap:12px;margin:28px 0}
.flow .fn{flex:1;background:var(--surface);border-radius:16px;padding:20px 14px;text-align:center;box-shadow:var(--sh-md);border:1px solid var(--line);position:relative;transition:.2s}
.flow .fn:hover{transform:translateY(-3px);box-shadow:var(--sh-lg)}
.flow .fn .fi{width:42px;height:42px;margin:0 auto 10px;border-radius:13px;background:var(--grad-soft);display:flex;align-items:center;justify-content:center}
.flow .fn .nm{font-weight:800;color:var(--ink);font-size:16px}
.flow .fn .ds{font-size:12px;color:var(--muted);margin-top:4px;line-height:1.45}
.flow .ar{display:flex;align-items:center;color:var(--violet);flex-shrink:0}

.pipe{display:flex;margin:26px 0;gap:8px}
.pipe .ps{flex:1;background:var(--surface);border-radius:14px;padding:16px 10px;text-align:center;box-shadow:var(--sh-sm);border:1px solid var(--line);position:relative}
.pipe .ps .pn{display:inline-flex;width:24px;height:24px;border-radius:8px;background:var(--grad);color:#fff;font-family:var(--mono);font-size:11px;font-weight:700;align-items:center;justify-content:center;margin-bottom:7px}
.pipe .ps .pt{font-weight:800;color:var(--ink);font-size:15px}
.pipe .ps .pd{font-size:11px;color:var(--muted);line-height:1.4;margin-top:3px}

.mods{display:grid;grid-template-columns:1fr 1fr;gap:14px;margin:26px 0}
.mod{background:var(--surface);border-radius:18px;padding:20px;position:relative;overflow:hidden;box-shadow:var(--sh-md);border:1px solid var(--line);transition:.22s}
.mod:hover{transform:translateY(-4px);box-shadow:var(--sh-lg)}
.mod .bn{position:absolute;top:14px;right:18px;font-size:40px;font-weight:850;line-height:1;background:var(--grad-soft);-webkit-background-clip:text;background-clip:text;-webkit-text-fill-color:transparent;opacity:.9}
.mod .n{font-size:11px;color:var(--violet);letter-spacing:.8px;font-weight:700;text-transform:uppercase}
.mod h4{margin:7px 0 6px;font-size:18px;color:var(--ink);font-weight:800}
.mod p{font-size:13px;color:var(--muted);margin:0;line-height:1.5}

.roles{display:grid;grid-template-columns:1fr 1fr;gap:11px;margin:24px 0}
.role{background:var(--surface);border-radius:14px;padding:14px 16px;font-size:14px;display:flex;gap:12px;align-items:flex-start;box-shadow:var(--sh-sm);border:1px solid var(--line);transition:.18s}
.role:hover{transform:translateY(-2px);box-shadow:var(--sh-md)}
.role .ri{width:26px;height:26px;border-radius:8px;background:var(--grad-soft);color:var(--indigo-d);font-family:var(--mono);font-size:11px;font-weight:700;display:flex;align-items:center;justify-content:center;flex-shrink:0;margin-top:1px}
.role b{color:var(--ink);font-weight:700}.role span{color:var(--muted)}

.reveal{background:var(--grad);color:#fff;border-radius:22px;padding:30px 32px;margin:26px 0;position:relative;overflow:hidden;box-shadow:var(--sh-lg)}
.reveal::before{content:"";position:absolute;right:-50px;top:-50px;width:200px;height:200px;border-radius:50%;background:radial-gradient(circle,rgba(255,255,255,.22),transparent 70%)}
.reveal::after{content:"";position:absolute;left:-30px;bottom:-60px;width:160px;height:160px;border-radius:50%;background:radial-gradient(circle,rgba(255,255,255,.12),transparent 70%)}
.reveal .k{font-size:11.5px;letter-spacing:1.5px;color:rgba(255,255,255,.8);text-transform:uppercase;font-weight:700;position:relative}
.reveal h3{font-size:27px;margin:10px 0;color:#fff;font-weight:820;letter-spacing:-.5px;position:relative}
.reveal h3 .en{font-weight:500;color:rgba(255,255,255,.78);font-size:16px;display:block;margin-top:3px;letter-spacing:0}
.reveal p{color:rgba(255,255,255,.92);font-size:15px;margin:8px 0 0;position:relative}
.reveal p b{color:#fff;font-weight:700}

.opt{display:flex;align-items:center;gap:13px;width:100%;text-align:left;background:var(--surface);border:1.5px solid var(--line);color:var(--ink);padding:15px 18px;border-radius:15px;margin:11px 0;cursor:pointer;font-size:15.5px;font-family:inherit;transition:.18s;box-shadow:var(--sh-sm)}
.opt:hover:not(:disabled){border-color:var(--indigo);transform:translateY(-2px);box-shadow:var(--sh-md)}
.opt .ol{width:28px;height:28px;border-radius:9px;background:var(--bg2);color:var(--muted);font-family:var(--mono);font-weight:700;display:flex;align-items:center;justify-content:center;flex-shrink:0;transition:.18s;font-size:13px}
.opt:hover:not(:disabled) .ol{background:var(--indigo-50);color:var(--indigo-d)}
.opt.correct{border-color:var(--green);background:var(--green-50)}.opt.correct .ol{background:var(--green);color:#fff}
.opt.wrong{border-color:var(--rose);background:var(--rose-50)}.opt.wrong .ol{background:var(--rose);color:#fff}
.fb{margin-top:16px;font-size:14.5px;color:var(--ink2);background:var(--green-50);border-radius:14px;padding:16px 19px;display:none;line-height:1.65;border:1px solid #c9ede0}
.fb.show{display:block;animation:rise .35s ease}
.fb b{color:var(--green-d)}

.cardtip{font-size:14.5px;color:var(--ink2);margin-bottom:8px}
.cards{display:grid;grid-template-columns:1fr 1fr;gap:14px;margin:22px 0}
.flip{perspective:1300px;height:150px;cursor:pointer}
.fin{position:relative;width:100%;height:100%;transition:transform .6s cubic-bezier(.4,0,.2,1);transform-style:preserve-3d}
.flip.on .fin{transform:rotateY(180deg)}
.face{position:absolute;inset:0;backface-visibility:hidden;border-radius:17px;padding:18px;display:flex;flex-direction:column;justify-content:center}
.front{background:var(--surface);box-shadow:var(--sh-md);border:1px solid var(--line)}
.front .qn{font-family:var(--mono);font-size:10.5px;color:var(--violet);letter-spacing:1px;font-weight:700}
.front .qt{font-size:17px;margin-top:8px;color:var(--ink);font-weight:800;line-height:1.35}
.front .h{position:absolute;bottom:13px;right:16px;font-size:11px;color:var(--faint)}
.back{background:var(--grad);color:#fff;transform:rotateY(180deg);font-size:14px;line-height:1.65;box-shadow:var(--sh-lg)}

.plan{margin:22px 0;display:flex;flex-direction:column;gap:10px}
.pl{display:flex;align-items:center;gap:15px;padding:15px 18px;background:var(--surface);border-radius:14px;box-shadow:var(--sh-sm);border:1px solid var(--line)}
.pl .d{font-size:13px;color:#fff;font-weight:700;white-space:nowrap;background:var(--grad);padding:5px 12px;border-radius:8px}
.pl .t{font-size:14.5px;color:var(--ink2)}

.term{border-bottom:1.5px dotted var(--violet);cursor:help;color:var(--indigo-d);font-weight:600}

.nav{position:sticky;bottom:0;z-index:50;background:rgba(245,246,251,.85);backdrop-filter:blur(16px) saturate(1.4);border-top:1px solid var(--line)}
.nav-in{max-width:var(--maxw);margin:0 auto;padding:14px 24px;display:flex;align-items:center;gap:14px;justify-content:space-between}
.btn-prev{background:var(--surface);border:1px solid var(--line2);color:var(--ink2);padding:12px 20px;border-radius:13px;cursor:pointer;font-size:14.5px;font-family:inherit;font-weight:600;transition:.16s;box-shadow:var(--sh-sm)}
.btn-prev:hover:not(:disabled){border-color:var(--indigo);color:var(--indigo-d)}
.btn-prev:disabled{opacity:.4;cursor:not-allowed}
.btn-next{background:var(--grad);border:none;color:#fff;padding:13px 32px;border-radius:13px;cursor:pointer;font-size:15px;font-family:inherit;font-weight:700;transition:.16s;box-shadow:var(--sh-glow)}
.btn-next:hover{transform:translateY(-2px);box-shadow:0 14px 32px rgba(99,102,241,.4)}
.nav-mid{display:flex;flex-direction:column;align-items:center;gap:3px}
.btn-speak{background:var(--surface);border:1px solid var(--line2);color:var(--indigo-d);padding:7px 15px;border-radius:999px;cursor:pointer;font-size:13px;font-family:inherit;font-weight:600;transition:.16s;white-space:nowrap;display:flex;align-items:center;gap:6px;box-shadow:var(--sh-sm)}
.btn-speak:hover{border-color:var(--indigo);background:var(--indigo-50)}
.btn-speak.on{background:var(--grad);color:#fff;border-color:transparent}
.hint-key{font-size:11px;color:var(--faint)}

.toast{position:fixed;top:78px;left:50%;transform:translateX(-50%) translateY(-14px);background:var(--green);color:#fff;padding:12px 28px;border-radius:999px;font-size:15px;font-weight:700;opacity:0;transition:.32s;z-index:200;pointer-events:none;box-shadow:0 12px 34px rgba(16,185,129,.4);display:flex;align-items:center;gap:8px}
.toast.show{opacity:1;transform:translateX(-50%) translateY(0)}
.toast.no{background:var(--rose);box-shadow:0 12px 34px rgba(244,63,94,.4)}

.tip{position:fixed;background:var(--ink);color:#fff;padding:10px 14px;border-radius:11px;font-size:13px;max-width:250px;z-index:300;pointer-events:none;opacity:0;transition:.15s;line-height:1.6;box-shadow:0 12px 34px rgba(0,0,0,.28)}
.tip.show{opacity:1}

.center{text-align:center;padding-top:8px}
.checkmark{width:84px;height:84px;margin:0 auto 20px;border-radius:26px;background:var(--grad);display:flex;align-items:center;justify-content:center;box-shadow:var(--sh-glow);animation:pop .6s cubic-bezier(.34,1.56,.64,1)}
@keyframes pop{0%{transform:scale(0) rotate(-12deg)}100%{transform:scale(1) rotate(0)}}
.restart{display:inline-flex;align-items:center;gap:8px;margin-top:12px;background:var(--surface);border:1px solid var(--line2);color:var(--indigo-d);padding:12px 26px;border-radius:13px;cursor:pointer;font-size:15px;font-family:inherit;font-weight:600;transition:.16s;box-shadow:var(--sh-sm)}
.restart:hover{border-color:var(--indigo);transform:translateY(-2px);box-shadow:var(--sh-md)}

.cover-badge{display:inline-flex;align-items:center;gap:8px;background:var(--surface);border:1px solid var(--line);padding:7px 15px 7px 9px;border-radius:999px;font-size:12.5px;color:var(--ink2);font-weight:600;margin-bottom:26px;box-shadow:var(--sh-sm)}
.cover-badge .mk{width:20px;height:20px;border-radius:6px;background:var(--grad);display:flex;align-items:center;justify-content:center}
.cover-meta{display:grid;grid-template-columns:repeat(3,1fr);gap:12px;margin-top:30px}
.cm{background:var(--surface);border:1px solid var(--line);border-radius:15px;padding:15px 16px;box-shadow:var(--sh-sm)}
.cm b{display:block;color:var(--ink);font-size:15px;font-weight:800;margin-bottom:2px}
.cm span{font-size:12px;color:var(--muted)}
.start-btn{display:inline-flex;align-items:center;gap:10px;margin-top:30px;background:var(--grad);color:#fff;border:none;padding:16px 36px;border-radius:16px;font-size:16.5px;font-weight:700;font-family:inherit;cursor:pointer;transition:.2s;box-shadow:var(--sh-glow)}
.start-btn:hover{transform:translateY(-3px);box-shadow:0 16px 40px rgba(99,102,241,.45)}

@media(max-width:680px){
  body{font-size:16px}
  .mods,.roles,.cards,.cover-meta{grid-template-columns:1fr}
  .logo .tt,.hint-key{display:none}.dots{display:none}
  .stage{padding:28px 16px 40px}
  .flow{flex-direction:column}.flow .ar{transform:rotate(90deg);justify-content:center;padding:2px}
  .pipe{flex-wrap:wrap}.pipe .ps{flex:1 1 40%}
  /* 手机端: 翻页栏不挤、视频不过高、按钮好点、标题不溢出 */
  .nav-in{padding:11px 13px;gap:9px}
  .btn-next{padding:13px 20px;font-size:14.5px}
  .btn-prev{padding:11px 14px;font-size:13.5px}
  .btn-speak{padding:6px 12px;font-size:12px}
  .vcard video{max-height:44vh}
  .start-btn{width:100%;justify-content:center;padding:15px;font-size:16px;margin-top:24px}
  h1.big{font-size:clamp(30px,8.5vw,42px);line-height:1.1}
  h2.q{font-size:clamp(22px,6vw,31px)}
  ul.steps li{padding:13px 16px 13px 50px;font-size:15px}
  /* 提示框手机端调透气: 图标缩小、间距加大、行高拉开,不挤成一团 */
  .callout{gap:12px;padding:16px 15px}
  .callout .ic{width:32px;height:32px}
  .callout .lbl{margin-bottom:7px;font-size:11px}
  .callout .bd{font-size:14.5px;line-height:1.75}
}