:root{font-family:Inter,system-ui,-apple-system,Segoe UI,Roboto,sans-serif;color:#1f2937;background:#f7f8fc}*{box-sizing:border-box}body{margin:0}.app-shell{max-width:760px;margin:0 auto;min-height:100vh;padding:1rem;display:grid;gap:1rem}.app-header{text-align:center}.app-header p{margin:0;font-size:.85rem;color:#6b7280}.app-header h1{margin:.25rem 0 0;font-size:clamp(1.5rem,5vw,2.2rem)}.module-tabs{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:.5rem}.module-tabs button,.card-nav button{border:1px solid #cbd5e1;background:#fff;border-radius:.75rem;padding:.7rem .8rem;font-weight:600}.module-tabs button.active{background:#1d4ed8;border-color:#1d4ed8;color:#fff}.module-info h2{margin:0;font-size:1.1rem}.module-info p{margin:.25rem 0 0;color:#6b7280}.flashcard{perspective:1000px;min-height:250px;width:100%;border:none;background:transparent;position:relative;cursor:pointer}.flashcard-side{position:absolute;top:0;right:0;bottom:0;left:0;border-radius:1rem;border:1px solid #cbd5e1;background:#fff;padding:1rem;display:grid;align-content:space-between;gap:.6rem;backface-visibility:hidden;transition:transform .4s}.flashcard-front{transform:rotateY(0)}.flashcard-back{transform:rotateY(180deg);background:#eff6ff}.flashcard.is-flipped .flashcard-front{transform:rotateY(180deg)}.flashcard.is-flipped .flashcard-back{transform:rotateY(360deg)}.flashcard h2{margin:0;font-size:1.05rem;line-height:1.45;text-align:left}.flashcard p,.flashcard small{margin:0;color:#6b7280;text-align:left}.card-nav{display:grid;grid-template-columns:1fr 1fr;gap:.6rem}@media (max-width: 560px){.module-tabs{grid-template-columns:1fr}.flashcard{min-height:280px}}