body {
    font-family: Arial, sans-serif;
    text-align: center;
    background-color: #f4f4f4;
    margin: 0;
    padding: 0;
}

.container {
    margin: 20px auto;
    width: 90%;
    max-width: 400px;
    padding: 20px;
    background-color: white;
    border-radius: 10px;
    box-shadow: 0px 0px 10px rgba(0, 0, 0, 0.1);
}

h1 {
    margin-bottom: 20px;
    font-size: 1.8em;
}

label {
    font-size: 1.2em;
    display: block;
    margin-bottom: 10px;
}

input[type="number"] {
    width: 80px;
    font-size: 1.2em;
    padding: 5px;
    margin-bottom: 20px;
    text-align: center;
}

button {
    font-size: 1.5em;
    padding: 10px 20px;
    border: none;
    background-color: #4CAF50;
    color: white;
    border-radius: 5px;
    cursor: pointer;
}

button:active {
    background-color: #45a049;
}

#display {
    font-size: 3em;
    margin: 20px 0;
    background-color: #f8f9fa;
    padding: 20px;
    border-radius: 10px;
    box-shadow: inset 0px 0px 10px rgba(0, 0, 0, 0.1);
}

/* Media Queries for Mobile */
@media (max-width: 600px) {
    h1 {
        font-size: 1.5em;
    }

    input[type="number"] {
        width: 60px;
        font-size: 1em;
    }

    button {
        font-size: 1.2em;
        padding: 10px 15px;
    }

    #display {
        font-size: 2.5em;
        padding: 15px;
    }
}