body {
    font-family: Arial, sans-serif;
    background: #1e1e1e;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
}

.calculator {
    background: #222;
    padding: 20px;
    border-radius: 12px;
    width: 300px;
}

#display {
    width: 100%;
    height: 60px;
    background: black;
    color: white;
    font-size: 28px;
    text-align: right;
    padding: 10px;
    border-radius: 8px;
    margin-bottom: 12px;
    border: none;
}

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

button {
    padding: 18px;
    font-size: 18px;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    background: #333;
    color: white;
}

button:active {
    background: #444;
}

.equal {
    background: orange;
    color: black;
}