How to edit spellcheck error css?

Custom CSS & Theme Design
1

Hello!

I know there already are topics about this, but nothing worked and they all habe closed, so I’m creating a new one.

I am looking for a way to change the css of the spellcheck errors. (Because I have trouble to see the red line under the text as I am visually impaired)

I already tried this:

.CodeMirror .cm-spell-error {
  color: rgb(227, 68, 103);
}

but it did not work.

Does anyone know how to do it?