Mobile header/menu changed after installation

Using The Minimal theme, I added this plugin to fix the excerpts so that they show h2 headings, etc. The plugin works great on a desktop and shows up great on mobile devices, but the menu and header have changed from what was originally on the mobile devices. The header font was red/pink, now it’s black. It’s almost as if the plugin somehow overrode the theme’s settings. Any suggestions on how to fix this? I uninstalled the plugin and the theme didn’t go back to the way it was. Any thoughts on how to fix this?

https://ww.wp.xz.cn/plugins/advanced-excerpt/