.lesson345{max-width:1280px;margin:auto;padding:40px max(22px,3vw) 0}.lesson345 .lesson-breadcrumb{font-size:.85rem;color:#bfd2d5;margin:12px 0 36px}.lesson345 .lesson-breadcrumb a{text-decoration:underline}.lesson345 .lesson-hero{display:grid;grid-template-columns:1.15fr 1fr;gap:clamp(24px,4vw,60px);align-items:center;padding:26px 0 40px}.lesson345 h1{font:clamp(42px,5.6vw,76px)/1.08 Georgia,serif;letter-spacing:-.035em;margin:20px 0}.lesson345 .lesson-hero p{font-size:18px;line-height:1.7}.lesson345 .lesson-hero figure{margin:0}.lesson345 .lesson-hero img{width:100%;height:auto;border-radius:10px}.lesson345 figcaption{font-size:.9rem;line-height:1.6;margin-top:12px;color:#bdd0d2}.lesson345 .lesson-facts{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:15px;padding:20px;border:1px solid #42606b;border-radius:10px;background:#11232e;margin:0 0 28px}.lesson345 .lesson-facts p{font-size:15px;line-height:1.6;margin:0}.lesson345 .lesson-facts strong{display:block;color:#eed2a4}.lesson345 .lesson-actions,.td-education .lesson-actions{display:flex;flex-wrap:wrap;gap:14px 22px;align-items:center;margin:22px 0}.lesson345 .lesson-actions a,.td-education .lesson-actions a,.td-education button{min-height:46px;white-space:normal}.lesson345 .lesson-license{padding:22px;border-left:3px solid #d9bf8b;background:#122a31;line-height:1.7}.lesson345 .lesson-nav{margin:28px 0 36px}.lesson345 .lesson-nav ul{display:flex;gap:12px 24px;flex-wrap:wrap;list-style:none;padding:0}.lesson345 a{color:#bce5dd;text-underline-offset:.2em}.lesson345 .button-light{color:#11222b}.lesson345 .lesson-nav a,.lesson345 .lesson-page a{text-decoration:underline}.lesson345 .lesson-page{padding:clamp(22px,3vw,42px);border:1px solid #3d5865;border-radius:10px;margin:28px 0;background:#0d1b24;scroll-margin-top:22px}.lesson345 .lesson-page h2{font:clamp(29px,3.4vw,43px)/1.15 Georgia,serif;margin:0 0 26px}.lesson345 .lesson-page h3{font-size:21px;line-height:1.4;margin:28px 0 14px;color:#bde8df}.lesson345 .lesson-page p{font-size:17px;line-height:1.78;max-width:80ch}.lesson345 .lesson-page>.eyebrow{font-size:12px;color:#e0c395;letter-spacing:.13em}.lesson345 .lesson-table{overflow-x:auto;border:1px solid #526a73;margin:22px 0;overscroll-behavior-x:contain}.lesson345 table{border-collapse:collapse;width:100%;min-width:560px;font-size:16px;line-height:1.6}.lesson345 caption{text-align:left;font-weight:650;padding:14px;color:#f0ede5;background:#102730}.lesson345 th,.lesson345 td{border:1px solid #526a73;padding:12px 14px;text-align:left;vertical-align:top}.lesson345 th{background:#17343d;color:#f0ede5;font-weight:650}.lesson345 .lesson-diagram{margin:24px 0;padding:18px;background:#fff;border:1px solid #9aafb4;border-radius:8px;color:#17303a}.lesson345 .lesson-diagram svg{display:block;width:100%;height:auto}.lesson345 .lesson-diagram figcaption{color:#17303a;font-size:15px;line-height:1.65}.lesson345 .lesson-formula{padding:15px 20px;border-left:3px solid #d9bf8b;background:#142c34;overflow-wrap:anywhere}.lesson345 .lesson-formula code{font:1rem/1.7 ui-monospace,monospace}.lesson345 .response-note{font-size:14px!important;color:#c1cdd1;font-style:italic}.lesson345 .lesson-resource-link{overflow-wrap:anywhere}.lesson345 .lesson-resource-link small{display:block;font-size:14px}.lesson345 .sr-only{position:absolute;width:1px;height:1px;overflow:hidden;clip-path:inset(50%);white-space:nowrap}.lesson345 :focus-visible,.td-education :focus-visible{outline:3px solid #f2cf8c;outline-offset:4px}.td-education{padding:clamp(24px,4vw,58px);border:1px solid #486574;border-radius:12px;background:linear-gradient(120deg,#112b35,#0c1822);margin:38px 0;scroll-margin-top:24px}.td-education h2{font:clamp(31px,4vw,52px)/1.12 Georgia,serif}.td-education h3{font-size:21px;color:#c0e9e2}.td-education p,.td-education li{font-size:17px;line-height:1.75;max-width:80ch}.td-education .lesson-mini-facts{color:#e3c395;font-size:15px}.td-education button{border:1px solid #a4c4c6;background:#c1e1d8;color:#10232d;padding:13px 20px;border-radius:5px;font:inherit;cursor:pointer}.td-education .lesson-status{min-height:1.8em;font-size:15px}.td-education [hidden]{display:none!important}
#teaching .button-light,#teaching .button-light:hover,#teaching .button-light:focus{color:#11222b}
@media(max-width:780px){.lesson345 .lesson-hero{grid-template-columns:1fr}.lesson345 .lesson-hero figure{max-width:580px}.lesson345 .lesson-facts{grid-template-columns:1fr}.lesson345 .lesson-page p{font-size:16px}.lesson345 .lesson-page{padding:20px}.lesson345 .lesson-actions a,.td-education .lesson-actions a{max-width:100%}.lesson345 table{font-size:15px}.lesson345 th,.lesson345 td{padding:10px}}
@media print{body{background:white!important;color:#17303a!important}.site-header,.noise,.footer,.analytics-consent,.newsletter-band,.share275,.lesson-nav,.lesson-hero,.lesson-facts,.lesson-breadcrumb,.lesson-actions,.response-note{display:none!important}.lesson345{max-width:none;margin:0;padding:0}.lesson345 .lesson-page{break-before:page;border:0;border-radius:0;background:white;color:#17303a;padding:0;margin:0}.lesson345 .lesson-page h2{font-size:23pt}.lesson345 .lesson-page h3{color:#17303a;font-size:12pt}.lesson345 .lesson-page p{font-size:10.5pt;line-height:1.45}.lesson345 .lesson-table{overflow:visible}.lesson345 table{min-width:0;font-size:9pt;line-height:1.4}.lesson345 th,.lesson345 td{padding:6pt;color:#17303a;background:white}.lesson345 caption{color:#17303a;background:white}.lesson345 .lesson-page a{color:#17303a}.lesson345 .lesson-formula{background:#eef3f3}.lesson345 .lesson-license{background:white;color:#17303a}.lesson345 .lesson-diagram{padding:0}.lesson345 .lesson-diagram figcaption{font-size:9pt}.lesson345 .lesson-diagram svg{max-height:150pt}.lesson345 .eyebrow{color:#17303a!important}}

/* Release 348: keep worldline labels readable without collisions on phones. */
.lesson345 .lesson-diagram{overflow-x:auto;overscroll-behavior-x:contain}
.lesson345 svg[aria-labelledby="td345-worldlines-title td345-worldlines-desc"]{min-width:680px}
@media print{.lesson345 .lesson-diagram{overflow:visible}.lesson345 svg[aria-labelledby="td345-worldlines-title td345-worldlines-desc"]{min-width:0}}

/* Release 349: classroom preset keeps dark text on an opaque pale button.
   The lab's general hover rule must not replace only its background. */
#teaching button[data-td-classroom]{background:#c1e1d8;color:#10232d;border-color:#a4c4c6}
#teaching button[data-td-classroom]:hover,
#teaching button[data-td-classroom]:focus-visible{background:#d8f2e9;color:#10232d;border-color:#d8f2e9}
#teaching button[data-td-classroom]:active{background:#afd8cb;color:#10232d;border-color:#afd8cb}
#teaching button[data-td-classroom]:focus-visible{outline:3px solid #f2cf8c;outline-offset:4px}