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

body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background: #1c1c1e;
    font-family: Arial, sans-serif;
}

.calculator {
    width: 320px;
    background: #2c2c2e;
    border-radius: 16px;
    padding: 16px;
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.4);
}

.title {
    text-align: center;
    color: #fff;
    font-size: 18px;
    font-weight: bold;
    letter-spacing: 3px;
    padding: 4px 0 16px;
}

.display {
    background: #000;
    color: #fff;
    font-size: 36px;
    text-align: right;
    padding: 16px;
    border-radius: 8px;
    margin-bottom: 16px;
    min-height: 72px;
    overflow: hidden;
    white-space: nowrap;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 8px;
}

.btn {
    font-size: 22px;
    padding: 16px;
    border: none;
    border-radius: 8px;
    background: #48484a;
    color: #fff;
    cursor: pointer;
    transition: background 0.15s;
}

.btn:hover {
    background: #5a5a5d;
}

.btn:active {
    background: #6f6f72;
}

.operator {
    background: #ff9500;
}

.operator:hover {
    background: #ffab3d;
}

.operator:active {
    background: #ffbe6b;
}

.equals {
    background: #ff9500;
}

.zero {
    grid-column: span 2;
}