/* General Reset */
* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

/* Body styling */
body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background: linear-gradient(135deg, #667eea, #764ba2);
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

/* Calculator container */
.calculator {
    background: #1e1e2f;
    padding: 30px 20px;
    border-radius: 25px;
    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.5);
    width: 320px;
}

/* Display */
.display {
    width: 100%;
    height: 60px;
    font-size: 2rem;
    text-align: right;
    padding: 10px;
    border: none;
    border-radius: 15px;
    margin-bottom: 20px;
    background: #2c2c3f;
    color: #fff;
}

/* Buttons grid */
.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 15px;
}

/* General button style */
button {
    padding: 20px;
    font-size: 1.4rem;
    border: none;
    border-radius: 15px;
    cursor: pointer;
    transition: 0.2s;
    box-shadow: 0 5px 10px rgba(0, 0, 0, 0.3);
}

/* Number buttons */
.btn {
    background: #2c2c3f;
    color: #fff;
}

/* Operator buttons */
.btn.operator {
    background: #ff9500;
    color: #fff;
}

/* Function buttons (C, DEL) */
.btn.function {
    background: #ff3b30;
    color: #fff;
}

/* Equal button */
.btn.equal {
    background: #34c759;
    color: #fff;
    grid-row: span 2;
}

/* Zero button spans two columns */
.btn.zero {
    grid-column: span 2;
}

/* Hover effects */
button:hover {
    filter: brightness(1.2);
}

/* Responsive */
@media (max-width: 400px) {
    .calculator {
        width: 90%;
        padding: 20px;
    }

    .display {
        font-size: 1.8rem;
        height: 50px;
    }

    button {
        padding: 15px;
        font-size: 1.2rem;
    }
}

/* Button press effect */
button:active {
    transform: scale(0.95);
    box-shadow: 0 3px 6px rgba(0,0,0,0.2);
}