/* C1: Cân bằng phương trình Hoá học */
.theme-thcs { background: linear-gradient(135deg, #e8eaf6 0%, #c5cae9 100%); }
.theme-thcs .game-header h1 { color: #283593; }

.equation-display {
    display: flex; align-items: center; justify-content: center; flex-wrap: wrap;
    gap: 8px; padding: 20px; margin: 20px auto; max-width: 600px;
    background: white; border-radius: 16px; box-shadow: 0 4px 20px rgba(0,0,0,0.08);
    min-height: 80px; font-size: 1.3rem; font-family: 'Nunito', sans-serif; font-weight: 700;
}
.eq-part { display: inline-flex; align-items: center; gap: 4px; }
.eq-coeff {
    width: 40px; height: 40px; border: 2px dashed #90caf9; border-radius: 10px;
    display: inline-flex; align-items: center; justify-content: center;
    font-size: 1.3rem; font-weight: 800; color: #1565c0; background: #e3f2fd;
    cursor: pointer; transition: all 0.2s; user-select: none;
}
.eq-coeff:hover { background: #bbdefb; transform: scale(1.1); }
.eq-coeff.active { border-color: #1565c0; background: #bbdefb; box-shadow: 0 0 0 3px rgba(21,101,192,0.2); }
.eq-coeff.correct { border-color: #4caf50; background: #e8f5e9; color: #2e7d32; }
.eq-coeff.wrong { border-color: #f44336; background: #ffebee; color: #c62828; animation: shake 0.4s; }
.eq-symbol { font-size: 1.5rem; color: #555; font-weight: 800; margin: 0 4px; }
.eq-formula { font-size: 1.3rem; color: #333; }
.eq-formula sub { font-size: 0.8rem; }

.coefficient-zone {
    display: flex; gap: 10px; justify-content: center; flex-wrap: wrap;
    margin: 15px auto; max-width: 350px;
}
.coeff-btn {
    width: 50px; height: 50px; border-radius: 12px; border: 2px solid #c5cae9;
    background: white; font-size: 1.4rem; font-weight: 800; color: #283593;
    cursor: pointer; transition: all 0.15s; font-family: 'Baloo 2', cursive;
    box-shadow: 0 3px 0 #9fa8da;
}
.coeff-btn:hover { background: #e8eaf6; transform: translateY(-2px); }
.coeff-btn:active { transform: translateY(3px); box-shadow: 0 0px 0 #9fa8da; }

.btn-check-eq {
    display: block; margin: 15px auto; padding: 12px 40px; border: none; border-radius: 99px;
    background: #4caf50; color: white; font-size: 1.3rem; font-family: 'Baloo 2', cursive;
    cursor: pointer; box-shadow: 0 5px 0 #2e7d32; transition: all 0.15s;
}
.btn-check-eq:hover { background: #43a047; }
.btn-check-eq:active { transform: translateY(5px); box-shadow: 0 0 0 #2e7d32; }

@keyframes shake {
    0%, 100% { transform: translateX(0); }
    25% { transform: translateX(-6px); }
    75% { transform: translateX(6px); }
}

@media (max-width: 500px) {
    .equation-display { font-size: 1.1rem; padding: 15px; }
    .eq-coeff { width: 35px; height: 35px; font-size: 1.1rem; }
    .coeff-btn { width: 44px; height: 44px; font-size: 1.2rem; }
}