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

.calculator {
    background: #fff;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.2);
    width: 40vw;
}

input {
    width: 100%;
    height: 50px;
    text-align: right;
    font-size: 20px;
    margin-bottom: 10px;
}

button {
    width: 23%;
    height: 50px;
    margin: 2px;
    font-size: 18px;
    border: none;
    border-radius: 5px;
    background: #eee;
    cursor: pointer;
}

button:active {
    background: #ddd;
}