Link colors don’t change when grouping

I would like to know how to change the link colors. The grouping option does not show how to change it for me, only allows changing the background and text (which only changes the color of the bullet points)

I believe it’s the same problem as in the topic https://wordpress.org/support/topic/simpletoc-link-color/
but I did not see a solution listed besides applying CSS, and I don’t know how to do it.
I would really appreciate assistance finding a way of doing this, as a wall of bright red links is not looking great now.

Thank you