internal server error and design problem

I am making corrections in the header section. When I press the publish button, the internal server error message appears and it does not update. I turn off all plugins one by one and try them, there is no plugin conflict, I try it in another theme and it is not related to the theme. PHP memory on the server side is also fine. Elementor plugin works fine. The same problem exists in the footer section.

Also, the header and footer sections are not displayed correctly. The fonts became larger at the top, and the text format and background colors at the bottom were distorted. I uninstalled the plugin and installed it twice, the same thing continues.

The page I need help with: [log in to see the link]