```css
/* Base theme colors */
:root {
    --primary-color: #4A90E2;
    --secondary-color: #50E3C2;
    --accent-color: #F5A623;
    --bg-light: #f9f9f9;
    --bg-dark: #333;
}

/* Typography and spacing */
body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    margin: 0;
    color: var(--bg-dark);
}

h1, h2, h3, h4 {
    color: var(--primary-color);
    margin-top: 0;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

header {
    background-color: var(--secondary-color);
    padding: 10px 0;
}

nav a {
    color: white;
    text-decoration: none;
    margin-left: 15px;
}

main {
    background-color: var(--bg-light);
    padding-bottom: 50px;
}

.hero {
    background-color: var(--accent-color);
    color: white;
    text-align: center;
    padding: 60px 20px;
}

.hero img {
    max-width: 100%;
    height: auto;
    margin-top: 15px;
}

.advantages, .about-preview, .testimonials, .faq-preview, .registration, .contact-details {
    padding: 50px 20px;
}

.grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 30px;
}

.advantage-card, .testimonial-card, .faq-item {
    background-color: white;
    padding: 20px;
    border-radius: 8px;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

.contact-info {
    margin-top: 20px;
    font-size: 0.9em;
}

.registration form {
    background-color: white;
    max-width: 500px;
    margin: 0 auto;
    padding: 30px;
    border-radius: 8px;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

label {
    font-weight: bold;
    display: block;
    margin-top: 10px;
}

input[type="text"], input[type="email"], input[type="tel"], input[type="checkbox"] {
    width: calc(100% - 20px);
    margin-top: 5px;
    padding: 8px;
    box-sizing: border-box;
}

button {
    background-color: var(--primary-color);
    color: white;
    border: none;
    padding: 10px 15px;
    margin-top: 15px;
    cursor: pointer;
    border-radius: 4px;
    width: 100%;
}

footer {
    background-color: var(--bg-dark);
    color: white;
    padding: 20px 0;
    text-align: center;
}

.footer-links {
    display: flex;
    justify-content: center;
    gap: 50px;
}

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

@media (max-width: 768px) {
    .footer-links {
        flex-direction: column;
        align-items: center;
    }
}
```