* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #f4f4f4;
    font-family: Arial, sans-serif;
}

.calculator {
    background-color: #333;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 0 20px rgba(0, 0, 0, 0.2);
}

.calculator h2 {
    color: #fff;
    text-align: center;
    margin-bottom: 20px;
}

.input-area {
    margin-bottom: 20px;
}

#display {
    width: 100%;
    padding: 15px;
    font-size: 1.5em;
    border: none;
    border-radius: 5px;
    text-align: right;
    background-color: #fff;
}

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

button {
    padding: 20px;
    font-size: 1.2em;
    border: none;
    border-radius: 5px;
    background-color: #0073e6;
    color: #fff;
    cursor: pointer;
    transition: background-color 0.3s ease;
}

button:hover {
    background-color: #005bb5;
}

.zero {
    grid-column: span 2;
}

.equals {
    background-color: #ffcc00;
}

.equals:hover {
    background-color: #e6b800;
}