```css
/* Base styles (mobile-first) */
:root {
    --primary-color: #3498db;
    --hover-color: #2980b9;
    --text-color: #333;
    --bg-color: #f9f9f9;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    font-size: 14px;
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--bg-color);
    margin: 0;
    padding: 0;
}

h1 {
    font-size: 24px;
    margin-bottom: 16px;
}

h2 {
    font-size: 22px;
    margin-bottom: 14px;
}

h3 {
    font-size: 20px;
    margin-bottom: 12px;
}

a {
    color: var(--primary-color);
    text-decoration: none;
    transition: color 300ms ease;
}

a:hover {
    color: var(--hover-color);
}

header, footer {
    background-color: white;
    padding: 20px;
    text-align: center;
}

nav ul {
    list-style: none;
    padding: 0;
}

nav li {
    display: block;
    margin: 10px 0;
}

.hero {
    text-align: center;
    padding: 20px;
}

.hero img {
    width: 100%;
    height: auto;
    margin: 20px 0;
}

.features {
    padding: 20px;
}

.feature {
    margin-bottom: 30px;
    text-align: center;
}

.feature i {
    font-size: 2em;
    color: var(--primary-color);
    margin-bottom: 10px;
}

.social {
    margin-top: 20px;
}

.social a {
    margin: 0 10px;
    font-size: 1.5em;
}

/* Media Queries */
@media (min-width: 640px) {
    nav li {
        display: inline;
        margin: 0 15px;
    }
}

@media (min-width: 768px) {
    body {
        font-size: 16px;
    }
    
    .features {
        display: flex;
        justify-content: space-between;
        flex-wrap: wrap;
    }
    
    .feature {
        width: 48%;
    }
}

@media (min-width: 1024px) {
    h1 {
        font-size: 28px;
    }
    
    h2 {
        font-size: 26px;
    }
    
    h3 {
        font-size: 24px;
    }
    
    .feature {
        width: 30%;
    }
}

@media (min-width: 1200px) {
    body {
        font-size: 18px;
    }
    
    main {
        max-width: 1200px;
        margin: 0 auto;
    }
}
```