.calculator {
    width: 320px;
    background-color: var(--app-container-bg-dark);
    border-radius: 10px;
    padding: 20px;
    box-shadow: 0 5px 15px rgba(0,0,0,0.2);
}
.display {
    background-color: #222;
    color: white;
    font-size: 2.5rem;
    padding: 1rem;
    text-align: right;
    border-radius: 5px;
    margin-bottom: 1rem;
}
.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}
.btn {
    font-size: 1.5rem;
    padding: 1rem;
}
.zero {
    grid-column: span 2;
}