.intro-lead{font-size:1.15rem;line-height:1.9;color:#243f50;border-left:4px solid #147d80;padding:2px 0 2px 20px;margin:1.5rem 0 2rem}
.bridge-jump{display:grid;grid-template-columns:repeat(4,1fr);gap:10px;margin:1.5rem 0}
.bridge-jump a{display:flex;flex-direction:column;gap:5px;padding:14px 10px;border:1px solid #c7d9dd;border-radius:9px;text-decoration:none;background:#f5fafb;color:#17495a;font-weight:700;text-align:center}
.bridge-jump small{font-size:.78rem;font-weight:400;color:#5b6f75}.bridge-jump a:hover,.bridge-jump a:focus-visible{background:#e5f4f1;outline:2px solid #197c80;outline-offset:2px}
.ch01-model{margin:1.2rem 0 1.8rem;border:1px solid #cededf;border-radius:12px;overflow:hidden;background:#f8fbfc}
.ch01-model iframe{width:100%;height:680px;border:0;display:block}.ch01-model .model-caption{padding:12px 18px;margin:0;border-top:1px solid #dce6e8;font-size:.88rem;line-height:1.6}
.ch01-model .model-caption a{font-weight:650}.ch01-note{padding:14px 18px;border-left:3px solid #178083;background:#f2f9f8;font-size:.94rem;margin:1.4rem 0}.ch01-note p:last-child{margin-bottom:0}
.ch01-life{padding:10px 16px;margin:1rem 0;border-left:3px solid #7253a4;background:#f8f5fc;color:#4c3d65;font-size:.95rem}.ch01-life strong{color:#6c4896}.ch01-life p:last-child{margin-bottom:0}
.ch01-process{display:grid;grid-template-columns:1fr;max-width:650px;margin:1.5rem auto;padding:0;list-style:none;counter-reset:flow}
.ch01-process li{position:relative;border:1px solid #b8d5d6;border-radius:10px;padding:15px 20px 15px 64px;background:#f7fbfb;margin-bottom:30px;counter-increment:flow}
.ch01-process li:before{content:counter(flow,decimal-leading-zero);position:absolute;left:18px;top:17px;color:#167778;font-weight:750;font-size:1.2rem}.ch01-process li:not(:last-child):after{content:'↓';position:absolute;bottom:-29px;left:50%;font-size:23px;color:#4f7f85}.ch01-process b{display:block;margin-bottom:5px}.ch01-process span{font-size:.9rem;color:#4d6670;line-height:1.7;display:block}.ch01-process .flow-return{font-size:.84rem;color:#a05b27;margin-top:7px}
.ch01-check{margin:1rem 0;padding:12px 16px;border:1px solid #d6e1e4;border-radius:8px}.ch01-check summary{font-weight:650;cursor:pointer}.ch01-check[open] summary{margin-bottom:12px}
.ch01-source{font-size:.84rem;color:#566b76;line-height:1.7}.ch01-source a{overflow-wrap:anywhere}.ch01-figure-note{font-size:.86rem;color:#5d6b74}.ch01-model figure{margin:0}
.ch01-history{list-style:none;margin:1.5rem 0;padding:0;display:grid;grid-template-columns:repeat(2,1fr);gap:15px}.ch01-history li{border-top:3px solid #237b83;background:#f7fafb;padding:15px 18px;border-radius:0 0 8px 8px}.ch01-history strong{display:block;font-size:1.65rem;color:#236c79}.ch01-history b{display:block;font-size:1.08rem;margin-bottom:6px}.ch01-history span{display:block;font-size:.91rem;line-height:1.8}.ch01-history a{font-size:.85rem}
@media(max-width:700px){.bridge-jump{grid-template-columns:repeat(2,1fr)}.ch01-model iframe{height:780px}.intro-lead{font-size:1.05rem}.ch01-process li{padding-left:54px}.ch01-model .model-caption{padding:10px}.ch01-history{grid-template-columns:1fr}}

.bridge-definition-cases{display:grid;grid-template-columns:1fr 1fr;gap:12px;margin:1.4rem 0}.bridge-definition-cases details{padding:16px;border:1px solid #c4d9d9;border-radius:10px;background:#f6fbfa}.bridge-definition-cases summary{cursor:pointer;color:#215762;font-weight:650;line-height:1.65}.bridge-definition-cases p{font-size:.94rem;line-height:1.85;margin:12px 0 0}@media(max-width:700px){.bridge-definition-cases{grid-template-columns:1fr}}

.ch01-lifecycle{max-width:850px}.ch01-lifecycle .stage-steps{display:grid;grid-template-columns:1fr 1fr;gap:8px;margin:12px 0}.ch01-lifecycle .stage-steps span{background:white;border:1px solid #d4e4e3;border-radius:6px;padding:8px 10px;font-size:.88rem;color:#32585e}.ch01-lifecycle .stage-steps span:before{content:"• ";color:#1a8483}.ch01-lifecycle li>b{font-size:1.1rem}.ch01-lifecycle li>span{font-size:.88rem}@media(max-width:600px){.ch01-lifecycle .stage-steps{grid-template-columns:1fr}.ch01-lifecycle li{padding:14px 13px 14px 49px}}

.ch01-collision-cases{display:grid;grid-template-columns:1fr 1fr;gap:24px;margin:1.4rem 0 1.8rem}.ch01-collision-cases article{min-width:0;border-top:3px solid #237b83;padding-top:12px}.ch01-collision-cases h4{font-size:1.12rem;margin:0 0 12px}.ch01-collision-cases .collision-location{padding:9px 12px;background:#eef5f5;line-height:1.65;font-size:.95rem}.collision-location strong{display:block;color:#236371}.ch01-collision-cases figure{margin:12px 0 15px}.ch01-collision-cases img{display:block;width:100%;height:240px;object-fit:contain;background:#f1f5f6}.ch01-collision-cases figcaption{font-size:.82rem;line-height:1.65;margin:7px 0;color:#566b76}.ch01-collision-cases p{font-size:.95rem;line-height:1.8}.ch01-collision-cases article>a{font-weight:650}@media(max-width:700px){.ch01-collision-cases{grid-template-columns:1fr;gap:24px}.ch01-collision-cases img{height:auto}.ch01-collision-cases figcaption{font-size:.9rem}}

.ch01-safety-grid,.ch01-material-grid{display:grid;grid-template-columns:1fr 1fr;gap:18px;margin:24px 0}.ch01-safety-grid article,.ch01-material-grid article{min-width:0;background:#f7faf9;border:1px solid #dbe8e5;border-radius:10px;padding:14px}.ch01-safety-grid img,.ch01-material-grid img{width:100%;height:auto;display:block}.ch01-safety-grid h4,.ch01-material-grid h3{font-size:1.05rem;margin:12px 0 8px}.ch01-safety-grid p,.ch01-material-grid p{font-size:.94rem;line-height:1.8;margin:0}.ch01-type-figure{margin:18px 0}.ch01-type-figure img{width:100%;height:auto;border-radius:10px;border:1px solid #e2e9e8}.ch01-type-figure figcaption{font-size:.86rem;color:#526c72;padding:9px 0}.ch01-mechanics{border-left:4px solid #80619f;background:#faf7fc}.ch01-mechanics summary{color:#6a498b}.ch01-collision-cases small{font-size:.82rem;color:#617278}@media(max-width:600px){.ch01-safety-grid,.ch01-material-grid{grid-template-columns:1fr}.ch01-source{font-size:.9rem}}
.ch01-real-figure,.ch01-scale-context,.ch01-protection{margin:1.5rem 0}.ch01-real-figure img,.ch01-scale-context img,.ch01-protection img{display:block;width:100%;max-height:420px;object-fit:contain;background:#f3f7f7;border:1px solid #d9e6e4;border-radius:8px}.ch01-real-figure figcaption,.ch01-scale-context figcaption,.ch01-protection figcaption{font-size:.91rem;line-height:1.75;color:#435f66;margin:10px 0}.ch01-real-figure small,.ch01-scale-context small,.photo-credit{display:block;color:#687a80;font-size:.76rem;margin-top:7px}.ch01-scale-context{border-left:3px solid #497b89;padding-left:20px}.ch01-scale-context figure,.ch01-protection figure{margin:0 0 1rem}.ch01-scale-context>p{font-size:.96rem}.ch01-material-grid img{height:255px;object-fit:contain;background:#edf3f2}.ch01-material-grid article{background:white}.ch01-protection{padding:20px;background:#f6f9f8;border-radius:10px}@media(max-width:600px){.ch01-scale-context{padding-left:12px}.ch01-material-grid img{height:auto;max-height:320px}.ch01-protection{padding:12px}.ch01-real-figure figcaption{font-size:.88rem}}
.ch01-scale-context{display:grid;grid-template-columns:repeat(auto-fit,minmax(min(100%,280px),1fr));gap:20px;align-items:start}.ch01-scale-context img{height:230px}.ch01-scale-context .scale-reading p{font-size:.92rem;line-height:1.8}