The simplest way to preview an HTML file inside a VS Code tab in GitHub Codespaces is to use the Live Preview extension by Microsoft.

1. Open the Extensions panel in VS Code.

2. Search for Live Preview (Microsoft) and install it.

3. Restart VS Code (if needed).

4. Open your index.html file. You’ll now see a “Live Preview” icon in the top-right corner of the editor.

5. Click it, and your HTML file will be rendered directly inside a VS Code tab.

This avoids switching to an external browser and lets you preview your page right inside Codespaces.