styles.css

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: Arial, sans-serif;
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #282c34;
}

.calculator {
    width: 310px;
    background: #1e1e1e;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0px 4px 10px rgba(0, 0, 0, 0.2);
}

#display {
    width: 100%;
    height: 60px;
    text-align: right;
    padding: 10px;
    font-size: 24px;
    border: none;
    outline: none;
    background: #2b2b2b;
    color: white;
    border-radius: 5px;
    margin-bottom: 10px;
}

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

.btn {
    width: 60px;
    height: 60px;
    font-size: 20px;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    background: #3b3b3b;
    color: white;
    transition: 0.2s;
}

.btn:hover {
    background: #4a4a4a;
}

.operator {
    background: #ff9800;
}

.operator:hover {
    background: #e68900;
}

.equal {
    background: #4caf50;
}

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

.zero {
    grid-column: span 2;
}