:root{--blue:#1967d2;--light:#e8f0fe;--ink:#202124;--muted:#5f6368;--line:#dadce0;--red:#b3261e;--paper:#f7f8fa}*{box-sizing:border-box}body{margin:0;background:var(--paper);color:var(--ink);font:16px/1.65 -apple-system,BlinkMacSystemFont,'Noto Sans TC','PingFang TC',sans-serif}button,select{font:inherit;color:inherit}button,a,select{-webkit-tap-highlight-color:transparent}button{background:white;border:1px solid var(--line);border-radius:24px;padding:9px 17px;cursor:pointer;line-height:1.4}button:hover{background:#f1f3f4;border-color:#bdc1c6}button:disabled{opacity:.4;cursor:default}button:focus-visible,a:focus-visible,select:focus-visible{outline:3px solid #4285f4;outline-offset:3px}a{color:var(--blue);text-underline-offset:4px}.primary,button[aria-pressed=true]{background:var(--blue);color:white;border-color:var(--blue)}.mast{display:flex;justify-content:space-between;align-items:center;padding:16px max(24px,calc((100vw - 1160px)/2));background:#fff;border-bottom:1px solid #eee;gap:16px}.mast>div{display:flex;align-items:center;gap:20px}.brand{text-decoration:none;font-weight:750;color:var(--ink)}.subtle{font-size:13px;white-space:nowrap}main{max-width:1160px;margin:auto;padding:0 24px}.opening{padding:42px 0 28px}.eyebrow{font-size:12px;letter-spacing:.07em;color:var(--blue);font-weight:700;margin:0 0 10px}h1{font-size:clamp(30px,4vw,44px);line-height:1.25;letter-spacing:-.03em;margin:0}h2{font-size:clamp(23px,3vw,31px);line-height:1.4;margin:0 0 10px}h3{font-size:19px;line-height:1.45;margin:0 0 8px}p{margin:0 0 14px}.opening>p:not(.eyebrow){margin:14px 0;color:var(--muted)}.scope{font-size:12px;color:var(--muted)}#chapters{display:grid;grid-template-columns:repeat(4,1fr);gap:8px;margin-bottom:16px}#chapters button{text-align:left;border-radius:12px;padding:15px;font-size:14px}#chapters span{display:block;font-size:11px;opacity:.8;margin-bottom:5px}.workspace{border:1px solid var(--line);background:#fff;border-radius:20px;padding:26px}#topics{display:flex;gap:8px;flex-wrap:wrap;border-bottom:1px solid #eee;padding-bottom:20px;margin-bottom:24px}#topics button{font-size:13px;padding:7px 13px}#topics button[aria-pressed=true]{background:var(--light);color:var(--blue);border-color:#aecbfa}.lesson-heading{max-width:810px;margin-bottom:25px}#intro{color:var(--muted);font-size:15px}.steps{display:grid;grid-template-columns:repeat(4,1fr);gap:8px;margin-bottom:12px}.steps button{font-size:13px;padding:11px 8px;border-radius:10px}.stepno{font-size:11px;margin-right:7px}.narrative{background:var(--light);padding:18px 22px;border-radius:12px;min-height:118px;margin-bottom:20px}.narrative p{font-size:14px;margin:0;color:#34435c}.narrative h3{font-size:18px}.controls{display:flex;align-items:center;gap:10px;flex-wrap:wrap;margin:16px 0 22px}.controls small{color:var(--muted);font-size:12px;margin-left:auto}.comparisons{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:16px}.comparisons.single{grid-template-columns:1fr}.side{border:1px solid var(--line);border-radius:14px;padding:20px;min-width:0}.side .sub{font-size:12px;color:var(--muted);min-height:40px;margin:0}.lane{position:relative;height:102px;margin:10px 0 4px;display:grid}.lane:before{content:'';position:absolute;left:var(--edge);right:var(--edge);top:33px;border-top:2px solid #c7d6ed}.node{text-align:center;position:relative;padding:51px 3px 0;font-size:12px;font-weight:600;line-height:1.4;overflow-wrap:anywhere}.node:before{content:'';position:absolute;width:10px;height:10px;border:2px solid #8aa6cf;background:#fff;border-radius:50%;top:28px;left:calc(50% - 7px)}.packet{position:absolute;top:18px;transform:translateX(-50%);background:var(--blue);color:white;min-width:30px;height:30px;padding:2px 6px;text-align:center;font:600 16px/26px sans-serif;border-radius:8px;box-shadow:0 0 0 5px white;z-index:2}.packet.warn{background:var(--red)}.fields{margin:0;font-size:13px}.field{display:grid;grid-template-columns:34% 1fr;gap:8px;padding:10px 8px;border-top:1px solid #edf0f3;min-height:45px;border-radius:5px}.field dt{color:var(--muted)}.field dd{margin:0;font-weight:550;overflow-wrap:anywhere}.field.changed{background:var(--light)}.side.warn .field.changed{background:#fce8e6}.legend{font-size:11px;color:var(--muted);margin-top:12px}.takeaway{border-left:3px solid var(--blue);padding:4px 0 4px 17px;margin:26px 0}.takeaway span{display:block;color:var(--blue);font-size:11px;margin-bottom:5px}.takeaway strong{font-size:17px;font-weight:600}.evidence{display:flex;justify-content:space-between;align-items:flex-start;gap:18px;border-top:1px solid #eee;padding-top:18px}.evidence button{font-size:12px;flex-shrink:0}.sources{display:flex;gap:8px 16px;flex-wrap:wrap;font-size:11px}.lesson-footer{display:flex;justify-content:space-between;align-items:center;gap:12px;margin-top:28px;border-top:1px solid #eee;padding-top:23px}.lesson-footer button{font-size:13px}.lesson-footer span{font-size:11px;color:var(--muted)}footer{text-align:center;font-size:11px;color:var(--muted);padding:28px 10px 40px}.mobile,.mobile-nav{display:none}.picker{display:flex;gap:8px;flex-wrap:wrap;margin-bottom:18px}.picker button{font-size:13px}.info-card{padding:22px;border:1px solid var(--line);border-radius:14px}.info-card p:last-child{margin-bottom:0}.info-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:14px;margin-top:20px}.info-grid>div{background:var(--paper);padding:18px;border-radius:10px;font-size:14px}.info-grid h3{font-size:13px;color:var(--blue)}.reading-list dt{font-weight:650;margin:16px 0 5px}.reading-list dd{margin:0 0 12px;color:var(--muted)}.notice{background:#f1f3f4;border-radius:10px;padding:14px 17px;font-size:13px;color:var(--muted);margin-top:16px}.decision-row{display:grid;grid-template-columns:130px 1fr;gap:12px;margin-bottom:20px}.decision-row>span{font-weight:600}.decision-row .picker{margin:0}.route{display:flex;justify-content:space-around;align-items:center;gap:8px;padding:26px 10px;background:var(--light);border-radius:12px;margin:20px 0;font-size:14px}.route span{max-width:30%;text-align:center}.result-list{padding-left:22px;margin:12px 0}.result-list li{margin-bottom:9px}.fake-screen{text-align:center;background:var(--paper);padding:27px;border-radius:10px;margin:14px 0}.fake-screen span{display:block;color:var(--muted);font-size:12px}.http{font-weight:700;font-size:14px;margin:16px 0 8px}.http.fail{color:var(--red)}pre{white-space:pre-wrap;overflow-wrap:anywhere;word-break:break-word;background:#f1f3f4;padding:14px;border-radius:8px;font-size:12px;line-height:1.65;margin:0}.proof-status{font-size:13px;margin:12px 0;color:var(--muted)}dialog{border:1px solid var(--line);border-radius:18px;padding:0;max-width:760px;width:calc(100% - 32px);max-height:85vh;color:var(--ink)}dialog::backdrop{background:#18223280}dialog>header{display:flex;align-items:center;justify-content:space-between;gap:15px;padding:20px 24px;border-bottom:1px solid var(--line);position:sticky;top:0;background:white;z-index:3}dialog h2{font-size:20px;margin:0}#dialogBody{padding:8px 24px 28px}#dialogBody section{padding-top:24px}#dialogBody p,#dialogBody dd{font-size:14px}#dialogBody img{max-width:100%;border:1px solid var(--line);border-radius:8px}#dialogBody .map-list{display:grid;gap:9px}#dialogBody .map-list a{font-size:14px;text-decoration:none;padding:10px 14px;background:var(--paper);border-radius:7px}.progressbar{height:3px;background:#e5eaf2;margin-top:12px;overflow:hidden}.progressbar span{display:block;background:var(--blue);height:100%;width:0}.reveal-title{color:var(--blue);font-size:12px;margin-bottom:8px}@media(max-width:700px){main{padding:0 14px}.mast{padding:12px 15px}.mast>div{gap:10px}.mast button{font-size:11px;padding:7px 10px}.brand{font-size:13px}.subtle{font-size:11px}.opening{padding:27px 4px 22px}.opening>p:not(.eyebrow){font-size:14px}.mobile{display:initial}#chapters{display:none}.mobile-nav{display:flex;gap:8px;margin-bottom:12px}.mobile-nav select{width:100%;min-width:0;border:1px solid var(--line);background:white;border-radius:10px;padding:10px;font-size:14px}.workspace{padding:18px 14px;border-radius:14px}#topics{display:grid;grid-template-columns:repeat(2,1fr);gap:7px;padding-bottom:16px;margin-bottom:20px}#topics button{font-size:12px;padding:9px 7px}.lesson-heading{margin-bottom:20px}h2{font-size:23px}#intro{font-size:14px}.steps{gap:5px}.steps button{font-size:11px;padding:9px 3px}.stepno{display:block;margin:0 0 3px}.narrative{padding:16px;min-height:142px}.narrative h3{font-size:17px}.narrative p{font-size:13px}.comparisons{grid-template-columns:1fr;gap:12px}.side{padding:16px}.side .sub{min-height:0}.lane{height:98px}.controls small{width:100%;margin-left:0}.controls button{font-size:12px}.field{font-size:12px;grid-template-columns:34% 1fr;min-height:42px}.takeaway strong{font-size:16px}.evidence{display:block}.evidence button{margin-top:15px}.info-grid{grid-template-columns:1fr;gap:10px}.info-grid>div{padding:15px}.info-card{padding:17px}.picker{gap:7px}.picker button{font-size:12px}.decision-row{grid-template-columns:1fr;gap:8px}.lesson-footer{gap:6px}.lesson-footer button{font-size:12px;padding:9px 10px}.lesson-footer span{font-size:10px}.route{font-size:12px;padding:23px 7px}dialog>header{padding:16px}#dialogBody{padding:3px 17px 24px}.scope{font-size:10px}}
@media(prefers-reduced-motion:reduce){*{scroll-behavior:auto!important;animation:none!important;transition:none!important}}

/* Keep the chapter and playback controls reachable while reading a long comparison. */
#chapters{position:sticky;top:0;z-index:5;background:var(--paper);padding:8px 0;margin-bottom:8px}.workspace{scroll-margin-top:110px}.opening{padding:26px 0 18px}.opening h1{font-size:36px}.controls{position:sticky;top:94px;z-index:4;background:#ffffffed;backdrop-filter:blur(12px);padding:10px 0;margin:0 0 14px;border-bottom:1px solid #edf0f3}.controls small{font-size:11px}.narrative{min-height:108px}.opening>p:not(.eyebrow){margin:10px 0}
@media(max-width:700px){.opening{padding:22px 4px 18px}.opening h1{font-size:30px}.mobile-nav{position:sticky;top:0;z-index:5;background:var(--paper);padding:8px 0}.workspace{scroll-margin-top:74px}.controls{top:66px;gap:7px}.controls small{display:none}.controls button{font-size:11px;padding:9px 11px}.narrative{min-height:130px}.lesson-footer #nextLesson{max-width:57%}}

/* Phone reachability: one scenario and one symptom at a time. */
.phone-views{border-bottom:1px solid var(--line);padding-bottom:16px}.phone-modes{display:grid;grid-template-columns:repeat(4,1fr)}.phone-modes button{font-size:12px;border-radius:10px;padding:12px 8px}.phone-power{display:flex;align-items:center;justify-content:space-between;gap:12px;margin:18px 0;font-size:13px}.phone-power>span{display:flex;align-items:center;gap:9px}.phone-power svg{width:29px;height:24px;fill:none;stroke:currentColor;stroke-width:2}.phone-power button{font-size:12px}.phone-url{background:var(--paper);padding:12px 15px;border-radius:8px}.phone-url span{display:block;font-size:11px;color:var(--muted)}.phone-url code{display:block;font-size:14px;overflow-wrap:anywhere}.phone-lane{height:174px;margin:18px 0 8px}.phone-lane:before{top:88px}.phone-lane .node{padding-top:111px;font-size:14px}.phone-lane .node:before{top:83px}.phone-lane .node svg{position:absolute;top:9px;left:calc(50% - 29px);width:58px;height:48px;fill:none;stroke:var(--blue);stroke-width:2.2;stroke-linecap:round;stroke-linejoin:round}.phone-lane .node small{display:block;font-size:11px;color:var(--muted);margin-top:4px}.phone-lane .packet{top:74px}.phone-lane.loopback:before{border-top-style:dashed;border-color:#dadce0}.phone-lane .node-off svg{stroke:#80868b}.phone-animation-controls{display:flex;gap:10px;flex-wrap:wrap;margin-bottom:15px}.phone-animation-controls button{font-size:13px}.phone-caption{background:var(--light);padding:15px 17px;border-radius:10px;min-height:105px}.phone-caption strong{font-size:15px}.phone-caption p{font-size:13px;margin:7px 0 0}.phone-outcome{padding:19px 0 8px}.phone-outcome>span{font-size:11px;display:block;color:var(--muted)}.phone-outcome>strong{font-size:22px;color:var(--blue)}.phone-outcome.blocked>strong{color:var(--red)}.phone-outcome p{font-size:14px;margin:7px 0}.phone-assumptions{font-size:12px;border-top:1px solid var(--line);padding-top:12px}.phone-assumptions summary{cursor:pointer;color:var(--blue);padding:4px 0}.phone-assumptions p{margin:10px 0 0;color:var(--muted)}.preview-facts{border:1px solid var(--line);border-radius:10px;padding:14px 17px;margin-top:22px;font-size:12px}.preview-facts strong{font-size:13px}.preview-facts p{color:var(--muted);margin:6px 0 0}.phone-symptoms button{font-size:13px}
@media(max-width:700px){.phone-modes{grid-template-columns:repeat(2,1fr)}.phone-modes button{font-size:11px;padding:11px 5px}.phone-power>span{flex-wrap:wrap;gap:5px;font-size:12px}.phone-power button{font-size:11px;padding:9px 10px;flex-shrink:0}.phone-url{padding:10px}.phone-url code{font-size:12px}.phone-lane{height:162px;margin-top:13px}.phone-lane .node{font-size:11px;padding-left:2px;padding-right:2px}.phone-lane .node small{font-size:10px}.phone-lane .node svg{width:43px;height:42px;left:calc(50% - 21.5px);top:17px}.phone-animation-controls button{font-size:12px;padding:9px 12px}.phone-caption{min-height:128px}.phone-caption strong{font-size:14px}.phone-outcome>strong{font-size:20px}.phone-outcome p{font-size:13px}.phone-symptoms{display:grid;grid-template-columns:1fr}.phone-symptoms button{font-size:12px}.preview-facts{font-size:11px}}