My suggestions:

Using bootstrap or another UI Framework would surely improve many things, from the UX/UI side. At least it will help until a pro UX can work on it a lot more.

Bootstrapping also will make you code better since the foundation of the code is well done. It also works on mobile and it's easy to catch up as well to tell other developers to manage our codebase, bootstrap has good documentation online and you can do, practically, almost all kind of UI compositions with JS.

After that, I would follow Google Pagespeed recomendations to reach the 100 points and have something like my blog wich loads in 300ms-500ms.