:root{--primary:#2563eb;--primary-dark:#1d4ed8;--light-bg:#f8fafc;--white:#ffffff;--dark-text:#0f172a;--light-text:#64748b;--correct:#10b981;--wrong:#ef4444}body{font-family:Inter,sans-serif;background-color:var(--light-bg);color:var(--dark-text);display:flex;justify-content:center;align-items:center;min-height:100vh;padding:20px;padding-bottom:85px}body.auth-loading{display:none}.premium-card{background:var(--white);border-radius:24px;box-shadow:0 10px 30px -5px rgba(0,0,0,.05),0 20px 40px -15px rgba(0,0,0,.05);border:1px solid rgba(226,232,240,.8);padding:40px;width:100%;max-width:800px;transition:all .3s ease}.option-btn{text-align:left;width:100%;padding:16px 20px;border:1px solid #e2e8f0;background-color:var(--white);color:var(--dark-text);border-radius:16px;cursor:pointer;transition:all .2s cubic-bezier(.4, 0, .2, 1);display:flex;align-items:center}.option-btn:hover:not([disabled]){transform:translateY(-2px);border-color:var(--primary);box-shadow:0 4px 12px rgba(37,99,235,.08);background-color:#f8fafc}.option-btn.correct-choice{background-color:#ecfdf5;border-color:var(--correct);color:#065f46}.option-btn.wrong-choice{background-color:#fff1f2;border-color:var(--wrong);color:#9f1239}.option-btn.selected-choice{background-color:#eff6ff;border-color:#3b82f6;color:#1e3a8a}.option-btn.selected-choice .option-badge{background-color:#3b82f6;color:#fff}.option-badge{width:32px;height:32px;border-radius:50%;background-color:#f1f5f9;color:var(--light-text);display:flex;align-items:center;justify-content:center;font-weight:700;font-size:14px;flex-shrink:0;margin-right:16px;transition:all .2s ease}.option-btn:hover:not([disabled]) .option-badge{background-color:#dbeafe;color:var(--primary)}.option-btn.correct-choice .option-badge{background-color:var(--correct);color:var(--white)}.option-btn.wrong-choice .option-badge{background-color:var(--wrong);color:var(--white)}.difficulty-card{text-align:center;padding:24px;border:1px solid #e2e8f0;border-radius:20px;cursor:pointer;transition:all .2s ease;background-color:var(--white);width:100%}.difficulty-card:hover{transform:translateY(-4px);box-shadow:0 8px 20px rgba(0,0,0,.06);border-color:var(--primary)}.bottom-nav{position:fixed;bottom:0;left:0;width:100%;height:65px;background-color:rgba(255,255,255,.95);backdrop-filter:blur(10px);border-top:1px solid #e2e8f0;box-shadow:0 -4px 20px rgba(0,0,0,.03);display:flex;justify-content:space-around;align-items:center;z-index:1000}.nav-link{display:flex;flex-direction:column;align-items:center;text-decoration:none;color:var(--light-text);font-size:12px;font-weight:600;transition:all .2s ease}.nav-link.active,.nav-link:hover{color:var(--primary)}.hide{display:none!important}@media (max-width:480px){.bottom-nav{height:58px}}