:root{color-scheme:light;--navy:#172846;--gold:#ad7c24;--paper:#f6f3ed}*{box-sizing:border-box}body{margin:0;background:var(--paper);color:var(--navy);font:1.05rem/1.55 system-ui,sans-serif}header{display:flex;justify-content:space-between;gap:1rem;align-items:center;padding:1rem clamp(1rem,4vw,4rem);background:#fff;border-bottom:1px solid #e1d7c7}header>a{font-weight:800}a{color:#173c6b;text-underline-offset:.2em}nav{display:flex;gap:1rem;flex-wrap:wrap}main{max-width:1200px;margin:auto;padding:clamp(1rem,3vw,2rem)}.intro{max-width:48rem;margin-bottom:1.5rem}.eyebrow{color:#78521c;font-weight:800;letter-spacing:.08em;font-size:.8rem}.layout{display:grid;grid-template-columns:minmax(0,1fr) minmax(320px,1fr);gap:1rem;align-items:start}.card{background:white;border:1px solid #e5dfd3;border-radius:1rem;padding:clamp(1rem,2.5vw,1.6rem)}h1{font-size:clamp(2rem,5vw,3.2rem);line-height:1.1;margin:.3rem 0 1rem}h2{line-height:1.2}.question{font-size:1.8rem;font-weight:750}.actions{display:flex;flex-wrap:wrap;gap:.6rem;margin:1rem 0}button,.links a{font:inherit;border:1px solid #6b7990;background:white;color:var(--navy);border-radius:.6rem;padding:.7rem 1rem;min-height:48px;cursor:pointer}.primary{background:var(--navy);color:white;border-color:var(--navy)}button:disabled{opacity:.5;cursor:default}:focus-visible{outline:3px solid #c57e13;outline-offset:3px}#feedback{min-height:2rem;font-weight:650}#hint-text{background:#faf3de;border-left:4px solid var(--gold);padding:.8rem}.note{font-size:.9rem;color:#465770}.calculator iframe{display:block;border:0;width:100%;height:640px}.next-lessons{margin-top:1rem}.links{display:flex;flex-wrap:wrap;gap:.6rem}.links a{display:inline-flex;align-items:center}footer{padding:2rem;text-align:center}.skip{position:absolute;left:-9999px}.skip:focus{left:1rem;top:1rem;background:#fff;z-index:2}@media(max-width:760px){.layout{grid-template-columns:1fr}.calculator iframe{height:700px}}@media(prefers-reduced-motion:reduce){*{scroll-behavior:auto!important}}