*,:after,:before{box-sizing:border-box;margin:0;padding:0}:root{--bg-base:#08081a;--bg-card:rgba(255,255,255,0.04);--bg-card-hover:rgba(255,255,255,0.08);--bg-glass:rgba(255,255,255,0.06);--border-glass:rgba(255,255,255,0.12);--cyan:#00f5ff;--lime:#b8ff3e;--coral:#ff6b6b;--violet:#b05cff;--amber:#ffbe0b;--mint:#00e676;--pink:#ff4d9e;--correct:#00e676;--incorrect:#ff4d6d;--neutral:rgba(255,255,255,0.12);--text-primary:#f0f0ff;--text-secondary:#9090b8;--text-muted:#5a5a7a;--radius-sm:8px;--radius-md:14px;--radius-lg:22px;--radius-xl:32px}html{scroll-behavior:smooth}body{background-color:var(--bg-base);background-image:radial-gradient(ellipse 80% 50% at 20% 10%,rgba(0,245,255,.07) 0,transparent 60%),radial-gradient(ellipse 60% 40% at 80% 80%,rgba(176,92,255,.07) 0,transparent 60%);background-attachment:fixed;color:var(--text-primary);font-family:Inter,-apple-system,BlinkMacSystemFont,Segoe 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32px;height:64px;background:rgba(8,8,26,.85);-webkit-backdrop-filter:blur(20px);backdrop-filter:blur(20px);border-bottom:1px solid var(--border-glass)}.nav-logo{font-size:1.2rem;font-weight:800;letter-spacing:-.5px}.nav-tag{font-size:.7rem;font-weight:600;color:var(--cyan);background:rgba(0,245,255,.1);border:1px solid rgba(0,245,255,.25);padding:2px 8px;border-radius:20px;letter-spacing:.5px;text-transform:uppercase}.nav-link{font-size:.85rem;font-weight:600;color:var(--text-secondary);text-decoration:none;padding:6px 14px;border-radius:var(--radius-sm);transition:color .2s,background .2s}.nav-link:hover{color:var(--text-primary);background:var(--bg-card)}.nav-signin-btn{font-size:.8rem;font-weight:600;color:var(--cyan);text-decoration:none;padding:5px 14px;border-radius:99px;border:1px solid rgba(0,245,255,.35);background:rgba(0,245,255,.07);transition:background .18s,border-color 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rgba(0,230,118,.3)}.difficulty-badge.INTERMEDIATE{background:rgba(255,190,11,.15);color:var(--amber);border:1px solid rgba(255,190,11,.3)}.difficulty-badge.ADVANCED{background:rgba(255,107,107,.15);color:var(--coral);border:1px solid rgba(255,107,107,.3)}.question-text{font-size:1.25rem;font-weight:700;line-height:1.5;color:var(--text-primary);letter-spacing:-.3px}.options-list{display:flex;flex-direction:column;gap:12px;margin-bottom:28px}.option-btn{width:100%;text-align:left;padding:16px 20px;border-radius:var(--radius-md);border:1px solid var(--border-glass);background:var(--bg-card);color:var(--text-primary);font-size:.95rem;cursor:pointer;display:flex;align-items:center;gap:14px;transition:all .18s 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h4{color:var(--correct)}.explanation-panel.incorrect-panel h4{color:var(--incorrect)}.option-row{display:flex;flex-direction:column;gap:6px}.option-explanation{font-size:.82rem;line-height:1.5;color:var(--text-muted);padding:0 4px 8px 52px;animation:fade-in .25s ease}.option-explanation--correct{color:var(--mint)}.option-explanation--incorrect{color:var(--coral)}.option-explanation--dimmed{color:var(--text-muted)}.explanation-text{font-size:.92rem;color:var(--text-secondary);line-height:1.7;margin-bottom:12px}.reference-link{font-size:.8rem;color:var(--cyan);text-decoration:none;display:inline-flex;align-items:center;gap:4px}.reference-link:hover{text-decoration:underline}.next-btn{width:100%;padding:15px;border-radius:var(--radius-md);border:1px solid rgba(0,245,255,.3);background:rgba(0,245,255,.08);color:var(--cyan);font-size:.95rem;font-weight:700;cursor:pointer;margin-top:16px;transition:all 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.2s}.btn-primary:hover{opacity:.88;transform:translateY(-1px)}.btn-ghost{padding:12px 28px;border-radius:40px;border:1px solid var(--border-glass);background:transparent;color:var(--text-secondary);font-weight:700;font-size:.9rem;cursor:pointer;text-decoration:none;display:inline-flex;align-items:center;transition:all .18s}.btn-ghost:hover{border-color:rgba(255,255,255,.25);color:var(--text-primary)}.loading-screen{min-height:60vh;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:16px;color:var(--text-muted)}.spinner{width:36px;height:36px;border:3px solid rgba(0,245,255,.15);border-top:3px solid var(--cyan);border-radius:50%;animation:spin .7s linear infinite}.error-box{padding:20px 24px;border-radius:var(--radius-md);background:rgba(255,77,109,.08);border:1px solid rgba(255,77,109,.25);color:var(--coral);font-size:.9rem;text-align:center}@keyframes spin{to{transform:rotate(1turn)}}@keyframes slideDown{0%{opacity:0;transform:translateY(-8px)}to{opacity:1;transform:translateY(0)}}@keyframes fadeIn{0%{opacity:0;transform:translateY(12px)}to{opacity:1;transform:translateY(0)}}.fade-in{animation:fadeIn .4s ease both}@media (max-width:640px){.nav{padding:0 16px}.hero{padding:48px 0 40px}.question-card{padding:24px 20px}.quiz-container{padding:24px 16px 60px}}.qb-layout{display:flex;min-height:calc(100vh - 64px);max-width:1400px;margin:0 auto;padding:24px 20px;gap:24px}.qb-sidebar{width:260px;flex-shrink:0;display:flex;flex-direction:column;gap:12px;position:-webkit-sticky;position:sticky;top:80px;align-self:flex-start;max-height:calc(100vh - 100px);overflow-y:auto}.qb-sidebar-header{display:flex;align-items:center;justify-content:space-between;padding:0 4px}.qb-sidebar-title{font-size:1rem;font-weight:700;letter-spacing:.04em;text-transform:uppercase}.qb-sidebar-count{font-size:.75rem;color:var(--text-muted);background:var(--bg-card);border:1px solid 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p{font-size:.9rem;color:var(--text-secondary);line-height:1.55}.login-link-btn{background:none;border:none;color:var(--cyan);font-size:.8rem;cursor:pointer;text-decoration:underline;padding:0;margin-top:4px}.login-error{padding:12px 14px;border-radius:var(--radius-sm);background:rgba(255,77,109,.08);border:1px solid rgba(255,77,109,.3);color:var(--coral);font-size:.85rem}