Font color changing

I love using TOC, I have a bit problem. My font color for h2, h3, h4 and so on become changing to be grey. It should be black just like on paragraph font color. This kind of color is not clear to see for me.

I have put additional css to change the font color on customize css but no effects, it still shows grey color.

Example of url: https://smartenglish.id/contoh-soal-reflexive-pronouns/

Anyone help please, thank you for your help.

The page I need help with: [log in to see the link]