Frontend
HTML
Sturucte and semantics, usability and accessibility makes a difference
CSS
From CSS grid and flex layouts to selectors from the farest corners. I do SCSS and sometimes BEM for better structure
JS
In the last couple of years I've been working a lot on my JS-skills so I can teach the fundementals and move forward to all the hip libraries. Good bases in Vanilla (>ES6) and my prefered library, Vue. But due to the jobmarket demand I've also picked up React