/* Tùy chỉnh CSS cho Máy tính */
body {
    font-family: 'Inter', sans-serif;
    background-color: #f0f4f8;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
}

.calculator {
    width: 100%;
    max-width: 380px;
    padding: 1rem;
    background-color: #334155;
    /* Slate-700 */
    box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.3), 0 10px 10px -5px rgba(0, 0, 0, 0.1);
    border-radius: 1.5rem;
    transform: scale(1);
    transition: transform 0.2s ease-in-out;
}

.calculator:active {
    transform: scale(0.99);
}

.calculator-display {
    background-color: #1e293b;
    /* Slate-800 */
    color: #f8fafc;
    /* White */
    font-size: 2.5rem;
    text-align: right;
    padding: 1rem 1.5rem;
    margin-bottom: 1rem;
    border-radius: 0.75rem;
    overflow-x: auto;
    white-space: nowrap;
    height: 5.5rem;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    align-items: flex-end;
    line-height: 1;
}

.calculator-keys {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 0.75rem;
}

.key {
    padding: 1.5rem 0.5rem;
    font-size: 1.5rem;
    font-weight: 600;
    border: none;
    border-radius: 9999px;
    /* Full rounded */
    cursor: pointer;
    transition: background-color 0.15s ease-in-out, transform 0.1s ease-in-out;
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.2), 0 2px 4px -2px rgba(0, 0, 0, 0.15);
}

/* Nút Số (Digits) */
.key-digit,
.key-decimal {
    background-color: #475569;
    /* Slate-600 */
    color: #f8fafc;
}

.key-digit:hover,
.key-decimal:hover {
    background-color: #64748b;
    /* Slate-500 */
}

.key-digit:active,
.key-decimal:active {
    transform: translateY(1px);
}

/* Nút Toán tử (Operators) */
.key-operator {
    background-color: #f97316;
    /* Orange-600 */
    color: #fff;
}

.key-operator:hover {
    background-color: #fb923c;
    /* Orange-500 */
}

.key-operator:active {

    transform: translateY(1px);
}

/* Nút Đặc biệt (AC/Equals) */
.key-ac {
    background-color: #ef4444;
    /* Red-500 */
    color: #fff;
}

.key-ac:hover {
    background-color: #f87171;
    /* Red-400 */
}

.key-ac:active {
    transform: translateY(1px);
}

.key-equals {
    background-color: #10b981;
    /* Emerald-500 */
    color: #fff;
    grid-column: span 2;
    /* Chiếm 2 cột */
}

.key-equals:hover {
    background-color: #34d399;
    /* Emerald-400 */
}

.key-equals:active {
    transform: translateY(1px);
}

/* Responsive design */
@media (max-width: 640px) {
    .calculator {
        max-width: 90%;
        margin: 1rem;
    }

    .calculator-display {
        font-size: 2rem;
    }

    .key {
        padding: 1rem 0.5rem;
        font-size: 1.25rem;
    }
}