Apple Notes font colors that work on both light and dark background

I have my iPhone and iPad set to a dark background theme, but my iMac is set to light. When I use Apple Notes, I used to be able to see the fonts changing... they looked white on the iPhone and iPad, and black on the iMac.

Not sure what I did when I was changing colors on some of the paragraph headers (picked three random colors that show up well on light and dark background) but some of these color changes also went to the paragraph text in random areas. Well... I made the mistake of trying to change them to white on the iPad, but now they are faint and hard to read on the light background of the iMac.

So my question is... how do I change the font color so it automatically changes to light fonts on the dark background, and dark on the light background? I'm hoping I can do this without starting from scratch since there is a lot of information on this particular note.

Thanks!