Since I lightened the background of my theme a little, in reading mode, the callout text become invisible while the background become almost invisible.
Did you do it through theme settings or customer CSS? If you use CSS, you can do the same for callouts. If it is through some theme settings, check if someone has had similar problems with using your theme.
You’ll need to change something in (like) this class …
I did change the color values in the css file manually and put them under a .theme-light block so I can select between dark and lighter mode quickly.
That did the trick but only in Live preview, not in Reading mode where the problem is.
Sorry if this is a noob question but how can I apply this change in Reading mode ?
Hmm, this is strange. On my side, changes are applied in Live and Reading mode. Check with the DevTools inspector to see if different variables are used for the callout when in Live and Reading mode.
Also, a tried and true troubleshooting technique: turn everything off and start enabling things slowly to see when the issue shows up.
For CSS, I’d comment out any custom CSS you have, and start uncommenting sections. When the issue shows up, you’ll know what section or exact rule/declaration that’s causing the issue.