.calculator {
    max-width: 420px;
    background: #fff;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 4px 10px rgba(0,0,0,0.1);
    margin: auto;
    font-family: Arial, sans-serif;
}
h2 { text-align: center; color: #2c3e50; }
label { font-weight: bold; margin-top: 10px; display: block; }
input, select {
    width: 100%;
    padding: 10px;
    margin-top: 5px;
    border-radius: 5px;
    border: 1px solid #ccc;
}
button {
    width: 100%;
    padding: 12px;
    margin-top: 15px;
    background: #27ae60;
    color: #fff;
    font-size: 16px;
    border: none;
    border-radius: 5px;
    cursor: pointer;
}
button:hover { background: #219150; }
.result {
    margin-top: 15px;
    padding: 10px;
    background: #ecf9f1;
    border-radius: 5px;
    text-align: center;
    font-weight: bold;
    color: #2c3e50;
}