body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: #f4f7f6;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
}
.container {
    background: white;
    padding: 2rem;
    border-radius: 10px;
    box-shadow: 0 4px 15px rgba(0,0,0,0.1);
    text-align: center;
    width: 350px;
}
.input-group { margin-bottom: 15px; text-align: left; }
input { width: 100%; padding: 8px; margin-top: 5px; box-sizing: border-box; }
.btn {
    background-color: #2c3e50;
    color: white;
    padding: 10px 20px;
    text-decoration: none;
    border-radius: 5px;
    display: inline-block;
    border: none;
    cursor: pointer;
}
.result { margin-top: 20px; color: #27ae60; font-weight: bold; }