The user wants me to create a single-page web app with a top-down alien shooter game using Phaser. I need to:

1. Create a self-contained index.html file
2. Use the pre-existing phaser.min.js library with a plain script src tag
3. Use only procedurally generated graphics (no external images/audio)
4. Implement:
   - WASD movement
   - Aim and fire at waves of aliens
   - Health system
   - Score system
   - Increasing difficulty

Let me create this game with all the features requested.

Done! I've created a complete top-down alien shooter game in a single self-contained `index.html` file. Here's what's included:

**Controls:**
- **WASD** - Move the player ship
- **Mouse** - Aim
- **Left Click** - Fire

**Features:**
- Procedurally generated graphics for all game elements (player ship, 3 alien types, bullets, explosions, powerups)
- Health system with visual health bar
- Score tracking
- Wave-based gameplay with increasing difficulty
- 3 alien types:
  - Type 1 (purple): Basic chaser, fast, low health
  - Type 2 (orange): Shooter, medium speed/health
  - Type 3 (blue): Tank, slow, high health, shoots frequently
- Powerup drops (health pickups)
- Particle explosion effects
- Visual feedback (flashing on damage, invincibility frames)
- Game over screen with restart option

The game uses the pre-provided `phaser.min.js` library and runs entirely client-side with no external resources.