body {
    font-family: sans-serif;
    margin: 50px;
    background-color: #f4f4f4;
}

.calculator-container {
    padding: 20px;
    border-radius: 15px;
    border: 1px solid #ccc;
    width: 300px;
    margin: auto;
    text-align: center;
    background-color: #fff;
    box-shadow: 2px 2px 5px rgba(0,0,0,0.1); /* A little touch of modernism */
}

input[type="number"] {
    width: 80px;
    padding: 8px;
    margin: 5px;
    border: 1px solid #ddd;
    border-radius: 4px; /* Slightly rounded corners */
}

span {
    font-size: 1.2em; /* Make the plus sign a bit bigger */
    font-weight: bold;
    margin: 0 5px;
}

button {
    padding: 10px 20px;
    background-color: #289aa7; /* A nice green color */
    color: white;
    border: none;
    border-radius: 5px; /* Rounded button */
    cursor: pointer;
    font-size: 1em;
    transition: background-color 0.2s ease-in-out; /* Smooth hover effect */
}

button:hover {
    background-color: #216088; /* Darker green on hover */
}