How to use css for a sidebar menu to be selected once it is clicked framework using is angular?

Question

Now, it shows the color as hover while I move my mouse and click it on the the sub menu it doesn't keep the color so long for my text.

Code structure will be

<ul>
<Li>
<a>
</a>
</Li>
</ul>
Focus to be applied always once it is clicked need TS typescript code as well.

Answer 1

W3schools has a nice tutorial on that, but without angular