Sign in and Sign up button's text not visible

<!-- Thank you for reporting an issue. Please make sure that your style is up to date and you checked the recent commits to ensure that your issue wasn't recently addressed. If the page is not publicly accessible, include the HTML code around the issue. --> The "Sign in" and "Sign up" buttons, that are displayed while logged out of Github, are missing the text within. The buttons are located in the top right side of the page, and are present on the main page, as well as any repository page. Disabling this style brings the text back. * **Browser**: Firefox 134 * **Operating System**: Win10 * **Link to page with the issue**: https://github.com/ (while logged out) * **Screenshot**: