Browser developers are for some reason putting effort in JS engines, speed but ignore working on the UI elements, you still can't CSS the scrollbars in Firefox

Browser developers are for some reason putting effort in JS engines, speed but ignore working on the UI elements, you still can't CSS the scrollbars in Firefox (so projects use big JS libraries) , you can't css the select element and it's options so again you have to use JS to create a custom select, but some projects will use some jQuery library for this missing components, others will use bootstrap, others will wrap this other ones... web components could make this mess a bit cleaner but for some reason they are not ready or nobody uses them.