Responsive Landing Page Generator

You are an expert front-end web developer with 10+ years of experience specializing in responsive design. Create a COMPLETE, fully functional, modern landing page using ONLY HTML5, CSS3 (including Flexbox/Grid), and vanilla JavaScript (NO frameworks like Bootstrap, React, etc.).

**Product/Service Details:**
- Name: [INSERT PRODUCT/SERVICE NAME]
- Description: [BRIEF 1-2 SENTENCE DESCRIPTION]
- Target Audience: [e.g., small business owners, developers]
- Key Features: [LIST 3-6 MAIN FEATURES]
- CTA: [e.g., Sign up for free trial, Buy now]

**Page Structure Requirements (MUST include all sections):**
1. **Hero Section**: Eye-catching headline, subheadline, primary CTA button, hero image/background.
2. **Features Section**: 3-6 feature cards with icons, titles, descriptions.
3. **About/How It Works**: 3-step process or benefits grid.
4. **Testimonials**: 3-4 customer quotes with photos/avatars.
5. **Pricing/CTA Section**: Tiered pricing or single CTA with benefits.
6. **Footer**: Links, social icons, copyright.

**Design Guidelines:**
- Fully responsive (mobile-first: <576px, tablet 576-992px, desktop >992px).
- Modern, minimalist UI with smooth animations (CSS transitions/JS).
- Color scheme: Primary [COLOR], Secondary [COLOR], Neutral tones.
- Google Fonts: Use 2 max (e.g., Inter, Poppins).
- Icons: Use Font Awesome or SVG (embed).
- Performance: Optimize images (use placeholders), <100KB total if possible.
- Accessibility: ARIA labels, semantic HTML, keyboard nav.
- Interactions: Navbar scroll effect, smooth scroll, form validation (email signup in hero/footer).

**Output Format:**
- Single HTML file with <style> and <script> embedded.
- Comment sections clearly.
- NO external links/resources (self-contained).
- Test on multiple devices (describe briefly).

Generate the code now!