:root {
    --primary-color: #2C3E50;
    --display-bg: #ECF0F1;
    --num-bg: #3498DB;
    --op-bg: #E74C3C;
    --func-bg: #2ECC71;
    --equal-bg: #F1C40F;
    --clear-bg: #95A5A6;
}

body {
    margin: 0;
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: var(--primary-color);
    font-family: Arial, sans-serif;
}

.calculator {
    background-color: #34495e;
    padding: 20px;
    border-radius: 15px;
    box-shadow: 0 0 20px rgba(0,0,0,0.3);
    max-width: 100%;
    width: 400px;
}

.display {
    margin-bottom: 20px;
}

#display {
    width: 100%;
    height: 60px;
    background-color: var(--display-bg);
    border: none;
    border-radius: 10px;
    font-size: 24px;
    text-align: right;
    padding: 10px;
    box-sizing: border-box;
    color: var(--primary-color);
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

button {
    padding: 20px;
    font-size: 18px;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    color: white;
    transition: transform 0.1s, opacity 0.1s;
}

button:active {
    transform: scale(0.95);
    opacity: 0.8;
}

.num {
    background-color: var(--num-bg);
}

.op {
    background-color: var(--op-bg);
}

.func {
    background-color: var(--func-bg);
}

.equal {
    background-color: var(--equal-bg);
    color: var(--primary-color);
}

.clear {
    background-color: var(--clear-bg);
}

@media (max-width: 480px) {
    .calculator {
        width: 95%;
        padding: 10px;
    }
    
    button {
        padding: 15px;
        font-size: 16px;
    }
}
