:root{color-scheme:light;--ink:#203e40;--green:#117b7c;--paper:#f6f7f1;--border:#d9e3dc}*{box-sizing:border-box}body{margin:0;background:var(--paper);color:var(--ink);font-family:system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;font-size:17px;line-height:1.65}a{color:#086b6c;text-underline-offset:3px}a:hover{color:#034849}button,input{font:inherit}a:focus-visible,button:focus-visible,input:focus-visible,summary:focus-visible{outline:3px solid #d28816;outline-offset:4px}.wrap{width:min(1120px,calc(100% - 40px));margin-inline:auto}.site-header{background:#fff;border-bottom:1px solid var(--border)}.header-inner{display:flex;justify-content:space-between;align-items:center;gap:20px;min-height:82px}.brand{font-size:27px;font-weight:800;text-decoration:none;color:var(--ink)}.brand span{color:var(--green)}nav a{margin-right:20px}.skip-link{position:absolute;top:-100px;left:16px;background:white;padding:12px;z-index:2}.skip-link:focus{top:10px}.breadcrumbs{font-size:14px;margin-top:28px}.breadcrumbs ol{display:flex;flex-wrap:wrap;gap:8px;padding:0;list-style:none}.breadcrumbs li+li:before{content:"/";margin-right:8px;color:#607573}.breadcrumbs a{margin:0}.intro{padding:28px 0 25px;max-width:850px}.eyebrow{font-size:12px;letter-spacing:.1em;font-weight:750;text-transform:uppercase;color:var(--green);margin:0 0 10px}h1{font-size:clamp(30px,5vw,48px);line-height:1.16;margin:0 0 20px;letter-spacing:-.025em}h2{font-size:25px;line-height:1.3;margin:0 0 16px}h3{font-size:19px;line-height:1.4;margin:0 0 10px}p{margin:0 0 16px}.lead{font-size:20px;color:#425e5b}.panel{background:#fff;border:1px solid var(--border);border-radius:18px;padding:28px;margin-bottom:22px}.lesson-layout{display:grid;grid-template-columns:minmax(0,1fr) 285px;gap:28px}.steps{padding-left:24px}.steps li{padding:5px 0}.example{background:#e8f3e9}.example-answer{font-size:24px;font-weight:700}.button{display:inline-block;padding:12px 19px;border:0;border-radius:10px;background:var(--green);color:#fff;text-decoration:none;font-weight:700;cursor:pointer;text-align:center}.button:hover{background:#085a5b;color:#fff}.related{padding-left:20px}.related li{margin:10px 0}.question{border-top:1px solid var(--border);padding:24px 0 4px}.answer-row{display:flex;gap:10px;margin-top:6px;flex-wrap:wrap}.answer-row input{width:160px;max-width:100%;border:1px solid #859c95;border-radius:8px;padding:10px}.practice-form label{font-weight:650}.feedback{margin-top:12px;font-weight:650;min-height:0}.feedback:empty{margin:0}.feedback[data-state="correct"]{color:#21632a}.feedback[data-state="retry"]{color:#8b4600}details{margin:14px 0}summary{cursor:pointer;font-weight:650}details p{padding-top:10px}.grade-nav{display:flex;gap:12px;flex-wrap:wrap;margin:10px 0 30px}.grade-nav a{padding:10px 20px;border:1px solid var(--border);border-radius:9px;margin:0;background:white}.grade-nav a[aria-current]{background:var(--green);color:white}.lesson-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:20px}.lesson-card{margin:0}.grade-section{margin-bottom:40px}.small{font-size:14px;color:#526963}.site-footer{padding-block:40px;border-top:1px solid var(--border);margin-top:40px}.site-footer nav{margin-bottom:20px}.array-model{margin:20px 0}.array-model div{display:flex;gap:14px;margin:12px 0}.array-model span{width:23px;height:23px;border-radius:50%;background:var(--green)}.fraction-model{max-width:420px;margin:20px 0}.fraction-model>div{display:flex;margin:12px 0;height:32px;border:1px solid var(--green)}.fraction-model span{flex:1;border-right:1px solid var(--green);background:white}.fraction-model span:last-child{border:0}.fraction-model .filled{background:#117b7c}@media(max-width:760px){.lesson-layout{grid-template-columns:1fr}.lesson-grid{grid-template-columns:1fr}.panel{padding:22px}.header-inner{align-items:flex-start;flex-direction:column;padding-block:16px;gap:8px}.header-inner nav{font-size:15px}.intro{padding-top:20px}.wrap{width:calc(100% - 28px)}}@media(prefers-reduced-motion:reduce){*{scroll-behavior:auto}}@media print{.site-header,.site-footer,aside,.practice-form,.breadcrumbs,.grade-nav{display:none}.wrap{width:100%}.lesson-layout{display:block}.panel{break-inside:avoid;background:white}.question{break-inside:avoid}details:not([open])>p{display:block}}
.worksheet-controls input{width:20px;height:20px;vertical-align:middle;margin-right:8px}.worksheet-controls label{display:block;margin-bottom:18px}.worksheet-questions ol{padding-left:28px}.worksheet-questions li{padding:10px 0}.worksheet-questions .work-space{min-height:64px;border-bottom:1px solid #d9e3dc}.worksheet-answer-key li{margin:14px 0}.worksheet-name{font-size:15px;border-bottom:1px solid var(--border);padding-bottom:14px}@media print{.worksheet-controls{display:none!important}.worksheet-page .intro{padding:0}.worksheet-page h1{font-size:24px}.worksheet-questions{border:0;padding:0;break-inside:auto}.worksheet-questions li{break-inside:avoid}.worksheet-answer-key{display:none!important}.print-answer-key .worksheet-answer-key{display:block!important;break-before:page;border:0;padding:0}.worksheet-answer-key summary{display:none}.worksheet-answer-key ol{display:block}.worksheet-page .lead{font-size:14px}.worksheet-page .work-space{min-height:46px}}