body {
    margin: 0;
    padding: 0;
    background: linear-gradient(to bottom right, #667eea, #764ba2);
    font-family: 'Segoe UI', sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
}

.calculator {
    background: #fff;
    border-radius: 20px;
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.2);
    padding: 20px;
    width: 320px;
    transition: transform 0.3s ease;
}

.display {
    background: #222;
    color: #0f0;
    font-size: 2.5rem;
    text-align: right;
    padding: 20px;
    border-radius: 12px;
    margin-bottom: 20px;
    overflow-x: auto;
}

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

.btn {
    background: #f1f3f6;
    border: none;
    border-radius: 12px;
    padding: 20px;
    font-size: 1.2rem;
    cursor: pointer;
    transition: all 0.2s ease;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

.btn:hover {
    background-color: #ddd;
    transform: scale(1.05);
}

.operator {
    background-color: #ffd54f;
}

.operator:hover {
    background-color: #ffc107;
}

.equal {
    background-color: #4caf50;
    color: white;
}

.equal:hover {
    background-color: #43a047;
}

.zero {
    grid-column: span 2;
}