I tried it with pure HTML but it seems HTML can’t handle spacers so it probably should be done CSS. I also tried adding another element that aligned to that side but it created multiple menus.
In that case, you probably have to dig into the theme’s CSS and fix the problem yourself. The developer tools of your favorite browser are a very useful tool in that context.
Actually, I’d not touch this theme with a ten-foot pole. It is based on an old version of bootstrap, it’s not maintained, and (due to bootstrap) it is full of bloat.
In any case, without seeing the site (aka your repository), I wouldn’t know where to look for the relevant settings either.
My repository isn’t too different from the original source. Only difference I made was to eliminate the aspect ratio and some playing on config file. So you can use the original source.
Did that, but no. This stuff is broken (and ugly). I’m not going to go there. Anyone using float for a menu in 2022 should go back to the drawing board (or a CSS 101 class, learning about flex and grid).