```css
/* Mobile-first approach */
body {
    font-size: 14px;
    line-height: 1.5;
    margin: 0;
    padding: 0;
    font-family: Arial, sans-serif;
}

.main-heading {
    font-size: 24px;
    margin-bottom: 1rem;
}

h2 {
    font-size: 22px;
}

h3 {
    font-size: 20px;
}

h4 {
    font-size: 18px;
}

header {
    padding: 1rem;
    text-align: center;
    background-color: #f8f9fa;
}

nav ul {
    list-style: none;
    padding: 0;
    display: flex;
    justify-content: center;
    gap: 1rem;
}

nav a {
    text-decoration: none;
    color: #333;
    transition: color 300ms ease;
}

nav a:hover {
    color: #007bff;
}

.hero {
    text-align: center;
    padding: 2rem 1rem;
}

.hero-image {
    width: 100%;
    height: auto;
    max-width: 800px;
    margin: 1rem auto;
    display: block;
}

.features {
    padding: 1rem;
    display: grid;
    gap: 2rem;
}

.feature {
    padding: 1rem;
    border-radius: 8px;
    background-color: #f8f9fa;
}

.feature-icon {
    font-size: 2rem;
    margin-bottom: 1rem;
    color: #007bff;
}

footer {
    padding: 2rem 1rem;
    text-align: center;
    background-color: #f8f9fa;
}

.social {
    display: flex;
    justify-content: center;
    gap: 1rem;
    margin-top: 1rem;
}

.social-icon {
    font-size: 1.5rem;
}

.social-link {
    color: #333;
    transition: color 300ms ease;
}

.social-link:hover {
    color: #007bff;
}

/* Tablet view */
@media (min-width: 768px) {
    body {
        font-size: 16px;
    }

    .features {
        grid-template-columns: repeat(2, 1fr);
    }
}

/* Desktop view */
@media (min-width: 1024px) {
    .main-heading {
        font-size: 28px;
    }

    .features {
        grid-template-columns: repeat(3, 1fr);
    }
}

/* Large desktop view */
@media (min-width: 1200px) {
    body {
        font-size: 18px;
    }
}
```