:root{--paper:#f7f3ea;--ink:#16231f;--forest:#173f37;--teal:#0b6859;--coral:#b95135;--amber:#e7a44a;--line:#d9d1c2;--white:#fffdf8;--muted:#66736f;--serif:Georgia,'Times New Roman',serif;--sans:Arial,Helvetica,sans-serif}
*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;background:var(--paper);color:var(--ink);font-family:var(--sans);font-size:16px;line-height:1.7}a{color:var(--teal);text-underline-offset:3px}.skip-link{position:absolute;left:-9999px}.skip-link:focus{left:12px;top:12px;z-index:20;padding:9px 13px;background:#fff;border:2px solid var(--forest)}
.lesson-header{position:sticky;top:0;z-index:10;display:flex;align-items:center;justify-content:space-between;gap:24px;padding:14px max(22px,calc((100vw - 1380px)/2));border-bottom:1px solid var(--line);background:rgba(247,243,234,.96);backdrop-filter:blur(12px)}.brand{display:flex;align-items:center;gap:11px;color:var(--ink);text-decoration:none}.brand-mark{display:grid;grid-template-columns:1fr 1fr;width:38px;height:38px;background:var(--forest);color:#fff}.brand-mark span{display:grid;place-items:center;border:1px solid #52756d;font-size:12px;font-weight:700;line-height:1}.brand strong{display:block;font-family:var(--serif);font-size:19px;line-height:1}.brand small{display:block;margin-top:3px;color:var(--muted);font-size:9px;font-weight:700;letter-spacing:.08em;text-transform:uppercase}.lesson-header nav{display:flex;align-items:center;gap:22px}.lesson-header nav a,.lesson-search-open{color:var(--ink);font-family:var(--sans);font-size:13px;font-weight:700;text-decoration:none}.lesson-header nav a:hover,.lesson-search-open:hover{color:var(--teal)}.lesson-search-open{padding:0;border:0;background:transparent;cursor:pointer}.support-button{padding:8px 12px;border:1px solid var(--forest)}
.visually-hidden{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}.global-search-dialog{width:min(760px,calc(100% - 32px));max-height:min(760px,calc(100vh - 40px));margin:auto;padding:0;border:1px solid #9e9586;background:var(--paper);box-shadow:16px 16px 0 rgba(16,47,41,.28);color:var(--ink)}.global-search-dialog::backdrop{background:rgba(12,31,27,.7);backdrop-filter:blur(3px)}.dialog-heading{display:flex;justify-content:space-between;gap:20px;padding:25px 26px 18px}.dialog-heading .rail-label{margin-bottom:4px}.dialog-heading h2{margin:0;font-family:var(--serif);font-size:30px;line-height:1.1}.search-dialog-close{align-self:flex-start;width:34px;height:34px;border:1px solid var(--line);background:var(--white);color:var(--ink);font-size:24px;line-height:1;cursor:pointer}.global-search-box{display:block;margin:0 26px}.global-search-input{width:100%;height:50px;padding:0 15px;border:1px solid #8f8779;border-radius:0;background:var(--white);color:var(--ink);font:14px var(--sans);outline:none}.global-search-input:focus{border-color:var(--teal);box-shadow:0 0 0 3px rgba(11,104,89,.15)}.global-search-status{margin:13px 26px;color:var(--muted);font-size:11px}.global-search-results{display:grid;grid-template-columns:1fr 1fr;gap:8px;max-height:480px;overflow-y:auto;padding:0 26px 26px}.global-search-result{min-height:150px;padding:15px;border:1px solid var(--line);background:var(--white);text-decoration:none}.global-search-result:hover{border-color:var(--teal)}.global-search-result span,.global-search-result strong,.global-search-result p{display:block}.global-search-result span{color:var(--coral);font-size:8px;font-weight:800;letter-spacing:.08em;text-transform:uppercase}.global-search-result strong{margin-top:9px;color:var(--ink);font-family:var(--serif);font-size:17px;line-height:1.2}.global-search-result p{display:-webkit-box;overflow:hidden;margin:7px 0 0!important;color:var(--muted);font-size:10px;line-height:1.5;-webkit-box-orient:vertical;-webkit-line-clamp:3}
.reader-shell{display:grid;grid-template-columns:240px minmax(0,760px) 220px;gap:44px;max-width:1380px;margin:0 auto;padding:46px 28px 80px}.topic-nav,.right-rail{align-self:start;position:sticky;top:96px}.topic-nav-label,.rail-label,.lesson-kicker{margin:0 0 13px;color:var(--coral);font-size:10px;font-weight:800;letter-spacing:.12em;text-transform:uppercase}.topic-nav h2{margin:0 0 18px;font-family:var(--serif);font-size:23px;line-height:1.15}.topic-nav ol{margin:0;padding:0;list-style:none;border-top:1px solid var(--line)}.topic-nav li{border-bottom:1px solid var(--line)}.topic-nav a{display:grid;grid-template-columns:25px 1fr;gap:6px;padding:10px 3px;color:#53615c;font-size:12px;line-height:1.35;text-decoration:none}.topic-nav a span{color:#9a624f;font-family:var(--serif)}.topic-nav a:hover,.topic-nav a[aria-current=page]{color:var(--teal);font-weight:700}.all-topics{display:inline-block;margin-top:16px;font-size:11px;font-weight:800;text-transform:uppercase;letter-spacing:.08em}
.lesson-main{min-width:0}.breadcrumbs{display:flex;flex-wrap:wrap;gap:7px;margin-bottom:28px;color:#75807c;font-size:11px}.breadcrumbs a{text-decoration:none}.lesson-title{margin:0 0 26px;font-family:var(--serif);font-size:clamp(39px,5vw,61px);font-weight:500;line-height:1.02;letter-spacing:-.035em}.lesson-deck{max-width:640px;margin:-12px 0 32px;color:var(--muted);font-size:16px}.lesson-meta{display:flex;gap:18px;margin:0 0 34px;padding:13px 0;border-top:1px solid var(--line);border-bottom:1px solid var(--line);color:#66736f;font-size:11px;font-weight:700;text-transform:uppercase;letter-spacing:.06em}
.lesson-content{font-size:16px;line-height:1.75}.lesson-content>*{max-width:100%}.lesson-content h1:first-child{display:none}.lesson-content h1,.lesson-content h2,.lesson-content h3,.lesson-content h4{margin-left:0!important;text-indent:0!important;font-family:var(--serif)!important;text-transform:none!important;text-shadow:none!important;letter-spacing:-.018em;color:var(--ink)!important;background:transparent!important}.lesson-content h1{margin:50px 0 18px!important;font-size:35px!important}.lesson-content h2{margin:46px 0 17px!important;padding-top:8px;border-top:3px solid var(--forest)!important;font-size:28px!important;line-height:1.2}.lesson-content h3{margin:34px 0 12px!important;font-size:22px!important;line-height:1.3}.lesson-content h4{margin:28px 0 10px!important;padding:10px 13px!important;background:#e7eee9!important;color:var(--forest)!important;font-family:var(--sans)!important;font-size:14px!important;font-weight:800!important}.lesson-content p,.lesson-content li,.lesson-content div{font-family:var(--sans)!important}.lesson-content p{margin:0 0 18px!important;text-indent:0!important}.lesson-content ul,.lesson-content ol{padding-left:25px}.lesson-content li{margin-bottom:8px}.lesson-content img{max-width:100%;height:auto}.lesson-content table{display:block;max-width:100%;overflow-x:auto;border-collapse:collapse}.lesson-content td,.lesson-content th{padding:8px;border:1px solid var(--line)}.lesson-content [class*=Equation],.lesson-content [class*=equation]{overflow-x:auto;margin:17px 0!important;padding:14px 18px!important;border-left:4px solid var(--amber);background:#f0eadf;font-family:'Courier New',monospace!important;font-size:17px!important;white-space:normal}.lesson-content [class*=Hint],.lesson-content [class*=hint]{padding:16px 18px!important;border-left:4px solid var(--coral);background:#fae9df}.lesson-content [class*=Heading]{font-weight:800}.lesson-content font{font-family:inherit!important}.lesson-content a{font-weight:700}
.pager{display:grid;grid-template-columns:1fr 1fr;gap:14px;margin-top:58px;padding-top:24px;border-top:1px solid var(--line)}.pager a{min-height:90px;padding:16px;border:1px solid var(--line);background:var(--white);text-decoration:none}.pager a:last-child{text-align:right}.pager small{display:block;color:var(--coral);font-size:9px;font-weight:800;letter-spacing:.1em;text-transform:uppercase}.pager strong{display:block;margin-top:6px;color:var(--ink);font-family:var(--serif);font-size:17px;line-height:1.25}.pager .disabled{opacity:.35}
.right-rail section{margin-bottom:28px}.toc{margin:0;padding:0;list-style:none;border-left:1px solid var(--line)}.toc li{margin:0}.toc a{display:block;padding:5px 0 5px 13px;color:#65716d;font-size:11px;line-height:1.4;text-decoration:none}.toc a:hover{color:var(--teal)}.support-card{padding:18px;border-top:4px solid var(--coral);background:var(--forest);color:#fff}.support-card h2{margin:0;font-family:var(--serif);font-size:21px;line-height:1.2}.support-card p{margin:9px 0 15px;color:#d7e2de;font-size:12px;line-height:1.5}.support-card a{display:inline-block;padding:8px 10px;background:#f1b15e;color:#20332e;font-size:11px;font-weight:800;text-decoration:none}.ad-wrap{min-height:250px;padding:8px;border:1px solid var(--line);background:#f1ede5;text-align:center}.ad-label{display:block;margin-bottom:8px;color:#9a9f9d;font-size:8px;letter-spacing:.12em;text-transform:uppercase}.ads-disabled .ad-wrap{display:none}
.support-page .reader-shell{grid-template-columns:190px minmax(0,840px);justify-content:center}.support-page .lesson-main{padding-bottom:50px}.site-footer{display:grid;grid-template-columns:1fr 1fr 1fr;gap:24px;align-items:center;padding:34px max(28px,calc((100vw - 1184px)/2));background:#132e29;color:#dce5e2;font-size:11px}.site-footer p{margin:0;color:#9fb2ac;text-align:center}.site-footer div{display:flex;justify-content:flex-end;gap:18px}.site-footer a{color:#dce5e2;text-decoration:none}
.resource-downloads{display:grid;grid-template-columns:repeat(3,1fr);gap:12px;margin-top:26px}.resource-card{min-height:145px;padding:18px;border:1px solid var(--line);background:var(--white);text-decoration:none;transition:transform .15s ease,box-shadow .15s ease}.resource-card:hover{transform:translate(-2px,-2px);box-shadow:5px 5px 0 #ded5c7}.resource-card span,.resource-card strong,.resource-card small{display:block}.resource-card span{color:var(--coral);font-size:8px;font-weight:800;letter-spacing:.1em;text-transform:uppercase}.resource-card strong{margin:16px 0 20px;color:var(--ink);font-family:var(--serif);font-size:18px;line-height:1.2}.resource-card small{color:var(--teal);font-size:10px;font-weight:800}
@media(max-width:1100px){.reader-shell{grid-template-columns:200px minmax(0,1fr)}.right-rail{position:static;grid-column:2;display:grid;grid-template-columns:1fr 1fr;gap:24px}.right-rail .ad-wrap{display:none}}
@media(max-width:760px){.lesson-header{position:static;padding:13px 18px}.lesson-header nav a:not(.support-button){display:none}.lesson-header nav{gap:14px}.lesson-search-open{font-size:12px}.brand small{display:none}.global-search-dialog{box-shadow:8px 8px 0 rgba(16,47,41,.28)}.dialog-heading{padding:20px 18px 14px}.global-search-box{margin:0 18px}.global-search-status{margin:11px 18px}.global-search-results{grid-template-columns:1fr;padding:0 18px 20px}.reader-shell,.support-page .reader-shell{display:block;padding:30px 20px 60px}.topic-nav{position:static;margin-bottom:36px;padding:18px;border:1px solid var(--line);background:#fffdf8}.topic-nav ol{display:none}.topic-nav.open ol{display:block}.topic-nav h2{margin-bottom:0;font-size:19px;cursor:pointer}.topic-nav h2:after{content:' +';color:var(--coral)}.topic-nav.open h2:after{content:' −'}.lesson-title{font-size:40px}.lesson-content{font-size:15px}.lesson-content h2{font-size:25px!important}.right-rail{display:block;margin-top:40px}.toc{columns:2}.pager{grid-template-columns:1fr}.resource-downloads{grid-template-columns:1fr 1fr}.site-footer{grid-template-columns:1fr;text-align:center}.site-footer div{justify-content:center}.site-footer p{display:none}}
@media(max-width:460px){.resource-downloads{grid-template-columns:1fr}}
@media print{.lesson-header,.topic-nav,.right-rail,.pager,.site-footer{display:none!important}.reader-shell{display:block;max-width:none;padding:0}.lesson-content{font-size:11pt}.lesson-title{font-size:27pt}}