body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #e0e0e0;
    margin: 0;
}

.calculator {
    background-color: #444;
    padding: 20px;
    border-radius: 15px;
    width: 320px;
    box-shadow: 0px 0px 20px 0px rgba(0, 0, 0, 0.5);
}

#display {
    width: 100%;
    height: 60px;
    background-color: #fff;
    color: #000;
    font-size: 2em;
    text-align: right;
    padding-right: 10px;
    border: none;
    border-radius: 10px;
    margin-bottom: 15px;
}

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

button {
    padding: 20px;
    font-size: 1.5em;
    border-radius: 10px;
    border: 1px solid #888;
    background-color: #ddd;
    color: black;
    cursor: pointer;
}

button:active {
    background-color: #bbb;
}

button:nth-child(3n+4) {
    background-color: #f68b1e;
    color: white;
}

button:nth-child(4n) {
    background-color: #f68b1e;
    color: white;
}

button#equal {
    background-color: #00a65a;
    color: white;
    grid-column: span 2;
}

button#clear {
    background-color: #ff4c4c;
    color: white;
}