:root {
    --primary-color: #007bff;
    --primary-color-hover: #0056b3;
    --background-color: #f4f7f9;
    --card-background: #ffffff;
    --text-color: #333;
    --light-gray: #e9ecef;
    --gray: #6c757d;
    --error-color: #dc3545;
    --success-color: #28a745;
    --font-family: 'Roboto', sans-serif;
    --box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
    --border-radius: 8px;
}

@font-face {
    font-family: 'Roboto';
    font-display: swap; 
    src: local('Roboto'),
         url('Roboto-Regular.woff') format('woff'),
         url('Roboto-Regular.eot') format('embedded-opentype');
  }

body {
    font-family: var(--font-family);
    background-color: var(--background-color);
    color: var(--text-color);
    margin: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 20px;
    box-sizing: border-box;
}

.container {
    background-color: var(--card-background);
    padding: 40px;
    border-radius: var(--border-radius);
    box-shadow: var(--box-shadow);
    max-width: 500px;
    width: 100%;
    text-align: center;
}

.header {
    margin-bottom: 30px;
}

.logo {
    width: 80px;
    margin-bottom: 15px;
}

h1 {
    margin: 0;
    font-weight: 600;
    font-size: 28px;
}

.main-content p {
    color: var(--gray);
    margin-bottom: 30px;
}

.form-group {
    margin-bottom: 20px;
    text-align: left;
}

.form-group label {
    display: block;
    margin-bottom: 8px;
    font-weight: 600;
}

.input-group {
    display: flex;
}

select, input[type="text"] {
    width: 100%;
    padding: 12px;
    border: 1px solid var(--light-gray);
    border-radius: var(--border-radius);
    font-size: 16px;
    font-family: var(--font-family);
    transition: border-color 0.3s, box-shadow 0.3s;
}

select:focus, input[type="text"]:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(0, 123, 255, 0.25);
}

#prefix {
    width: auto;
    border-top-right-radius: 0;
    border-bottom-right-radius: 0;
    border-right: none;
}

#serial-number {
    border-top-left-radius: 0;
    border-bottom-left-radius: 0;
}

.error-message {
    color: var(--error-color);
    font-size: 14px;
    margin-top: 5px;
    min-height: 1em;
}

.changelog-links {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    justify-content: center;
    margin-top: 20px;
    margin-bottom: 30px;
}

.changelog-links a {
    color: var(--primary-color);
    text-decoration: none;
    font-size: 14px;
    padding: 5px 10px;
    border: 1px solid var(--primary-color);
    border-radius: var(--border-radius);
    transition: background-color 0.3s, color 0.3s;
}

.changelog-links a:hover {
    background-color: var(--primary-color);
    color: var(--card-background);
}

.btn-download {
    width: 100%;
    padding: 15px;
    background-color: var(--primary-color);
    color: white;
    border: none;
    border-radius: var(--border-radius);
    font-size: 18px;
    font-weight: 600;
    cursor: pointer;
    transition: background-color 0.3s, transform 0.2s;
}

.btn-download:hover {
    background-color: var(--primary-color-hover);
    transform: translateY(-2px);
}

.footer {
    margin-top: 30px;
    font-size: 14px;
    color: var(--gray);
}

.footer a {
    color: var(--gray);
    text-decoration: none;
}

.footer a:hover {
    text-decoration: underline;
    color: var(--primary-color);
}

@media (max-width: 576px) {
    .container {
        padding: 20px;
    }

    h1 {
        font-size: 24px;
    }
}