Rendering differences in headings and code

Thank you for this very useful package! I'm noticing a few differences in rendering via grip versus on GitHub. For the example README.md on my test-grip repo (file also attached below), the Level 1 and 2 headings rendered via grip lack the horizontal rules, and the code lacks the grey background shown on GitHub.

To render the README via grip, I'm running grip README.md in RStudio's Terminal. I'm running RStudio 2024.09.1 Build 394, R 4.4.0, and Python 3.13.7 on Windows 11 Enterprise (Ver. 10.0.22631 Build 22631). The rendering via grip looks the same regardless of whether I open the link to the Flask development server in Firefox (Ver. 142.0.1) or Chrome (Ver. 140.0.7339.128).

README.md

Rendered on GitHub:

Rendered via grip: