We appreciate the feedback! (Designer of the RBlind themes here).
We originally wanted to increase the thickness of the lines (and change the colour) of the post nesting next to comments, however these elements in particular are hard coded outside of all CSS themes and are inserted by some dynamic code that will “count” the number of comments in order to nest them correctly and add the style accordingly. So it is a limitation we cannot change (yet).
We’ve made a Github Issue about this, requesting for the lemmy-ui to define the thickness and colour inside CSS so theme developers can edit them: Define comment tree post left-border colour in CSS #2890 and Define comment tree post left-border width in CSS #2889. Once lemmy-ui address this issue we will be able to style the comment nesting border differently.
I would personally really like to change this as in web design it is best practice to separate style from function and for the most part the Lemmy CSS themes do this, but this is one area where they don’t.
Heya anniemdi, the latest version of the themes have a different colour designation for OP as well as more obvious comment and thread dividers.