I have a really hard time picking out the "background colors" in the app from the dark theme. Some customization here could definitely help me find a color that "popped"... or basically gives me a chance to see where my headers are in the first place.

Just gonna comment here to state that yes we need a dark mode without the blue tint please.

There's an accessibility benefit from heavily extensible themes. I'm old so I need higher contrast and larger font sizes, and ideally some fonts with easily distinguished elements like Atkinson Hyperlegible or OpenDyslexic. I also benefit from more easily distinguished headings (distinct colors, greater size differences, maybe a level indicator), possibly due to ADHD. Making each of these separate user-configurable options would be a nightmare to use and a nightmare to maintain. That's why themes are nice.

I wouldn't expect or want you folks already doing excellent programming work on a cleanly structured application to add "UX and Accessibility Expert" to their job duties. That's why user-defined themes are nice.

This can be tweaked a bit with browser extensions, but those don't carry over from work environment to the next, and they don't help in the desktop app. That's why persistent user-defined themes are nice.

Even a small start could improve things. Define some global CSS variables, or document existing ones. Provide a CSS snippet uploader in advanced user settings. Include user-defined snippets on page load wherever that user may be – except maybe the mobile app. I'm not unreasonable. Gradually add more CSS variables as you're more confident the solution is working. If and when you're ready, provide a means to share, search, and install CSS snippets as themes.

I'm a sucker for themes as I feel they greatly impact the way we feel and think about what's in front of us. Something like a color picker for the background and text, and a dropdown menu for the font would be pretty cool; that way you don't have to worry about crafting your own themes. The ability to use our own fonts that we download would be excellent.

Yea I would love a default grey with black text or the ability to set the default text color to a grey instead of white in settings somewhere.

Developers, please just be sure and put decent class IDs on tags, so that easy CSS customization is possible. While themes would be great at large, if there is an easy facility to tweak CSS, then just about anything is possible to accomodate the picky user ;-)

I mean, handcrafted themes are all great and everything, but people will always want some control over their personal space and I think they should have it.

The current themes are very low contrast in many areas, and this can cause headaches and other issues for users. I find the text boxes particularly hard to discern, and I'm not colour-blind. I also like coloured headings to help with hierarchy.

I think whatever themes are available, you should use a colour checker (for my work I use colorshark or coolors regularly) to make sure they will be accessible if you aren't going to make them customisable.

The WCAG guidelines would probably be useful to bear in mind: https://www.w3.org/WAI/standards-guidelines/wcag/