:root{--bg: #f8fafc;--surface: #ffffff;--text: #0f172a;--muted: #475569;--ok: #166534;--ok-bg: #dcfce7;--err: #991b1b;--err-bg: #fee2e2;--amber: #b45309;--amber-bg: #fef3c7;--primary: #0f766e;--ring: #0ea5e9;--radius: 12px}*{box-sizing:border-box}body{margin:0;font-family:Trebuchet MS,Segoe UI,sans-serif;background:linear-gradient(180deg,#e0f2fe 0%,var(--bg) 45%);color:var(--text);min-height:100vh}.app-shell{max-width:680px;margin:0 auto;padding:1rem}.screen{background:var(--surface);border-radius:var(--radius);padding:1rem;box-shadow:0 10px 24px #0f172a14}.hidden{display:none}.config-grid{display:grid;gap:.5rem;margin-bottom:1rem}label{font-weight:700}select,input,button{font:inherit}select,input{width:100%;padding:.65rem;border-radius:10px;border:1px solid #94a3b8}button{border:0;border-radius:10px;padding:.7rem 1rem;background:var(--primary);color:#fff;font-weight:700;cursor:pointer}button:focus-visible,select:focus-visible,input:focus-visible{outline:3px solid var(--ring);outline-offset:2px}#exam-screen:not(.hidden){display:flex;flex-direction:column;gap:1rem}.exam-header{display:flex;justify-content:flex-end}#timer{font-size:1.2rem;font-weight:700;padding:.35rem .6rem;border-radius:8px;background:#ecfeff}.operation{font-size:1.8rem;font-weight:800;margin:1rem 0;text-align:center}.message{min-height:1.8rem;border-radius:8px;padding:.45rem .6rem;margin-top:.7rem;font-weight:700}.error:not(:empty){color:var(--err);background:var(--err-bg)}.feedback[data-result=correct]{color:var(--ok);background:var(--ok-bg)}.feedback[data-result=wrong]{color:var(--err);background:var(--err-bg)}#result-screen[data-result-color=red]{background:var(--err-bg);color:var(--err)}#result-screen[data-result-color=amber]{background:var(--amber-bg);color:var(--amber)}#result-screen[data-result-color=green]{background:var(--ok-bg);color:var(--ok)}@media(min-width:720px){.app-shell{padding:2rem 1.25rem}.screen{padding:1.5rem}}