Safari not rendering Markdown editor icons correctly

Some of the icons in the Markdown editor are missing in recent Safari versions on macOS:

<img width="1642" height="166" alt="Image" src="https://github.com/user-attachments/assets/aa3e0632-83cd-4545-a89d-6510bfe996fe" />

This is what it looks like in other browsers:
<img width="2284" height="180" alt="Image" src="https://github.com/user-attachments/assets/4c1a27af-a861-4066-8887-16955f4d1c1e" />