*{box-sizing:border-box}
:root{--accent:#0f766e;--accent2:#115e59;--bg:#f7faf9;--card:#fff;--text:#17302e;--muted:#607471;--line:#d9e5e2;--soft:#e7f3f1;--warn:#fff7df;--good:#e8f6ed}
html{scroll-behavior:smooth}
body{margin:0;background:var(--bg);color:var(--text);font-family:system-ui,-apple-system,Segoe UI,Roboto,Arial,sans-serif;font-size:16px;line-height:1.65}
button,input,select,textarea{font:inherit}
button,a{touch-action:manipulation}
.topbar{position:sticky;top:0;z-index:20;background:rgba(255,255,255,.96);backdrop-filter:blur(10px);border-bottom:1px solid var(--line);display:flex;justify-content:space-between;align-items:center;padding:12px 16px}
.brand{display:flex;gap:10px;align-items:center}.brand-mark{width:38px;height:38px;border-radius:12px;background:var(--accent);color:#fff;display:grid;place-items:center;font-weight:800}.brand-title{font-weight:750}.brand-subtitle{font-size:.78rem;color:var(--muted)}
.icon-btn{border:1px solid var(--line);background:#fff;border-radius:10px;padding:8px 11px;cursor:pointer}
.mobile-nav{display:none;position:sticky;top:63px;z-index:19;background:#fff;border-bottom:1px solid var(--line);padding:8px 16px}.mobile-nav.open{display:grid;grid-template-columns:1fr 1fr}.mobile-nav a{padding:9px;color:var(--text);text-decoration:none;border-radius:8px}.mobile-nav a:hover{background:var(--soft)}
main{max-width:760px;margin:auto;padding-bottom:30px}
.hero{padding:34px 18px 28px;background:linear-gradient(180deg,#eaf7f4 0,#f7faf9 100%);border-bottom:1px solid var(--line)}
.eyebrow{font-size:.75rem;font-weight:800;letter-spacing:.08em;color:var(--accent)}
h1{font-size:clamp(2rem,8vw,3.2rem);line-height:1.05;margin:8px 0 14px;letter-spacing:-.04em}
.big-question{font-size:1.1rem;max-width:650px;margin:0 0 20px;color:#274845}
.hero-actions{display:flex;flex-wrap:wrap;gap:9px}.btn{display:inline-flex;align-items:center;justify-content:center;border-radius:12px;padding:10px 14px;border:1px solid var(--line);text-decoration:none;cursor:pointer;font-weight:700}.btn.primary{background:var(--accent);color:#fff;border-color:var(--accent)}.btn.secondary{background:#fff;color:var(--accent)}.btn.small{font-size:.88rem;padding:7px 10px}
.section{padding:28px 18px;border-bottom:1px solid var(--line)}
.section.tinted{background:#eef7f5}
.section-heading{display:flex;gap:12px;align-items:flex-start;margin-bottom:18px}.section-heading h2{margin:0;font-size:1.45rem;line-height:1.2}.section-heading p{margin:3px 0 0;color:var(--muted)}.step{min-width:38px;height:38px;border-radius:11px;background:var(--soft);color:var(--accent);display:grid;place-items:center;font-weight:800;font-size:.82rem}
.outcomes{display:grid;gap:10px}.outcomes label,.project-checks label{display:block;background:var(--card);border:1px solid var(--line);padding:11px 12px;border-radius:12px}.outcomes input,.project-checks input{margin-right:9px}
.story,.think-box,.lesson-card,.investigation,.reason-card,.challenge-box,.project{background:var(--card);border:1px solid var(--line);border-radius:16px;padding:18px;margin-bottom:14px}
.think-box{background:var(--warn)}.think-box h3{margin-top:0}.prediction-grid{display:grid;gap:9px}.prediction{border:1px solid #e6d9a9;background:#fff;padding:12px;border-radius:11px;text-align:left;cursor:pointer;color:var(--text)}
.feedback{margin-top:12px;padding:11px 12px;border-radius:10px;background:var(--soft);min-height:20px}
.lesson-card h3,.investigation h3,.project h3{margin-top:0}.lesson-card h4{margin:8px 0}
.example-row{display:flex;flex-wrap:wrap;gap:9px;align-items:center;justify-content:center;background:#f4f8f7;border-radius:12px;padding:13px;margin:12px 0}.example-row div{padding:7px 10px;border-radius:9px;background:#fff;border:1px solid var(--line)}.example-row small{display:block;color:var(--muted);font-size:.75rem}.example-row span{font-weight:700}
.compare{display:grid;grid-template-columns:1fr 1fr;gap:12px}.compare>div{border:1px solid var(--line);border-radius:12px;padding:12px}.visual{height:95px;border-radius:10px;border:1px solid #b9cfcb;position:relative;overflow:hidden;background:#dff0ed}.uniform:after{content:"";position:absolute;inset:0;background:radial-gradient(circle,#fff 1px,transparent 2px);background-size:12px 12px;opacity:.6}.layers{background:linear-gradient(#e8f4f2 0 47%,#c8a97d 47% 100%)}.layers i{position:absolute;top:45%;width:100%;border-top:2px solid #b78d5e}
.mini-activity{margin-top:12px;padding:11px;background:var(--soft);border-radius:10px}.mini-activity .btn{margin-top:8px}
.formula{display:flex;gap:7px;justify-content:center;align-items:center;flex-wrap:wrap;margin:16px 0}.chip{padding:6px 10px;background:#e9eeed;border-radius:999px;font-weight:700}.chip.accent{background:var(--accent);color:#fff}
.settle-demo{display:flex;gap:20px;align-items:center;flex-wrap:wrap}.jar{width:110px;height:145px;border:3px solid #7fa7a1;border-radius:18px 18px 22px 22px;position:relative;overflow:hidden;background:#f8fcfb}.jar-liquid{position:absolute;inset:22px 0 0;background:#d9ebe8}.sediment{position:absolute;bottom:0;left:0;right:0;height:28px;background:#a17a4e}.particles{position:absolute;width:8px;height:8px;border-radius:50%;background:#8c6a45}.p1{left:30px;top:70px}.p2{left:67px;top:85px}.p3{left:48px;top:105px}
.light-demo{position:relative;height:120px;background:#152323;border-radius:12px;overflow:hidden;color:#d8f2ef;padding:15px}.beam{position:absolute;left:-20px;top:45px;width:100%;height:18px;background:rgba(255,255,255,.28);transform:rotate(-12deg)}.dust{position:absolute;left:38%;top:38%;letter-spacing:7px}
table{width:100%;border-collapse:collapse;margin-top:14px;font-size:.92rem}th,td{border:1px solid var(--line);padding:9px;text-align:left;vertical-align:top}th{background:#f0f6f4}
.method-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:10px}.method{background:#fff;border:1px solid var(--line);border-radius:12px;padding:13px;text-align:left;cursor:pointer}.method strong,.method span{display:block}.method span{color:var(--muted);font-size:.82rem;margin-top:3px}
ol{padding-left:22px}.observation-table{display:grid;gap:8px;margin:15px 0}.observation-table label{display:flex;align-items:center;justify-content:space-between;gap:10px}.observation-table select{border:1px solid var(--line);border-radius:9px;padding:8px;max-width:190px;background:#fff}.flow{display:flex;gap:7px;align-items:center;flex-wrap:wrap;justify-content:center;margin:18px 0}.node{padding:9px 11px;border:1px solid var(--line);border-radius:10px;background:#f7fbfa}.callout,.remember{background:var(--soft);padding:13px;border-radius:12px;border-left:4px solid var(--accent)}
.distill-steps{display:grid;grid-template-columns:repeat(5,1fr);gap:8px}.distill-steps>div{background:#f4f8f7;border:1px solid var(--line);border-radius:11px;padding:10px;text-align:center}.distill-steps b{display:grid;place-items:center;width:28px;height:28px;margin:0 auto 7px;border-radius:50%;background:var(--accent);color:#fff}
textarea{width:100%;min-height:110px;border:1px solid var(--line);border-radius:11px;padding:11px;resize:vertical;background:#fff}
.community-grid{display:grid;grid-template-columns:repeat(2,1fr);gap:10px}.community-card{border:1px solid var(--line);background:#fff;border-radius:13px;padding:13px}.community-card p{margin:4px 0 0;color:var(--muted);font-size:.93rem}
.project-checks{display:grid;gap:8px}.word-grid{display:grid;grid-template-columns:repeat(2,1fr);gap:9px}.word-grid div{border:1px solid var(--line);background:#fff;border-radius:11px;padding:11px}.word-grid span{display:block;color:var(--muted);font-size:.9rem;margin-top:2px}
.quiz-section{background:#f0f7f5}.quiz-q{background:#fff;border:1px solid var(--line);border-radius:14px;padding:15px;margin-bottom:11px}.quiz-q p{margin-top:0;font-weight:700}.quiz-options{display:grid;gap:7px}.quiz-options label{border:1px solid var(--line);border-radius:9px;padding:9px;cursor:pointer}.quiz-options label:has(input:checked){border-color:var(--accent);background:var(--soft)}.quiz-result{margin-top:14px;font-size:1.05rem;font-weight:700}
.report-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:8px}.report-grid span{background:#f5f9f8;border:1px solid var(--line);border-radius:9px;padding:9px;text-align:center;font-size:.9rem}
.accordion{display:grid;gap:7px}.accordion-btn{display:flex;justify-content:space-between;width:100%;background:#fff;border:1px solid var(--line);padding:13px;border-radius:11px;text-align:left;font-weight:750;cursor:pointer}.accordion-panel{display:none;background:#fff;border:1px solid var(--line);border-top:0;padding:14px;border-radius:0 0 11px 11px;margin-top:-7px}.accordion-panel.open{display:block}
.key-points{display:grid;gap:7px;padding-left:22px}.remember{margin-top:20px}.remember span{font-size:.75rem;font-weight:900;letter-spacing:.08em;color:var(--accent)}.remember p{font-size:1.05rem;font-weight:700;margin-bottom:0}
footer{padding:24px 18px;text-align:center;color:var(--muted);font-size:.9rem}

@media(max-width:520px){.compare,.community-grid,.word-grid{grid-template-columns:1fr}.method-grid{grid-template-columns:1fr}.distill-steps{grid-template-columns:1fr 1fr}.report-grid{grid-template-columns:1fr 1fr}.observation-table label{align-items:flex-start;flex-direction:column}.observation-table select{max-width:none;width:100%}}
@media(min-width:700px){.mobile-nav{display:flex;gap:4px;justify-content:center;top:63px}.mobile-nav a{padding:7px 10px}.icon-btn{display:none}}