I'm a back-end developer trying to improve my front-end skills, is there any good website that I can replicate/remake so I can improve my skills?

Keeps on repeatjng css and js basic, how far are you planning on doing front end? Do you need to get to framework stuff?

First learn HTML, when to use which element etc. Most devs don't do this correctly.

Start out with plain CSS and JavaScript and focus on Chrome, Firefox and Edge. Firefox and Edge follow the standards a bit better than Chrome but chrome is widely used. Ignore IE and safari for now.

Learn BEM

Then setup a taskrunner and precompiler like webpack and Babel.
Learn Sass/Scss or Less

Chiming in on starting with plain HTML. You'll eventually be using a concoction of frameworks, but you can tell when a site is made by someone who jumped straight into some single-page framework without knowing basic HTML first.

I've seen Vue components layered with a styling framework which was made to look and function like plain html using CSS overrides.

Sometimes - usually - all you need is basic CSS grid. I swear some of these frameworks effectively just rename the grid variable names.

https://developer.mozilla.org/en-US...

That's all just technical stuff though. If you're looking for guidance on style/ux I can't think of any resources from the top of my head.