Creating custom CSS for beginners

ELI5, how to create and active custom CSS to work inside a rem. I saw ton of videos on youtube, and read bit, but some reason, I just cant seem to get it to work. Can some one walk me through step by step, what I should do

here is what I have done so far.

  1. Went to Custom CSS under Settings> interface
  2. Created a blank CSS block
  3. type in the code block
    that’s its, I don’t know how to activate it from here inside a rem (or universally activate it across all rems)

added questions
i) also I don’t know whats the different between CSS Block vs CSS Template
ii) my CSS code block/ template gets checkbox todo icon and when I click it, it marks it as completed. I- Not sure if I should check it or leave it unchecked.

sample CSS code block I used below

#hierarchy-editor.TreeNode {
border-color: transparent;
border-width: 1px!important;

You’ve done everything correctly.

If your selector is targeting an element that is always active, it’s also always active. You may also create specialised selectors that will only work on rem that are tagged with a certain rem that has some text (defined in the CSS block).

CSS Templates are for Theme creation, i.e., as a template to restyle the whole app.

If you check it, you disable it (and any descendant CSS Code Blocks).