That makes no sense The search plugin has nothing to do with themes or skins. Do you have any errors in your logs after you disable the plugin and restart the forum? What about when you run ./nodebb build and restart is everything working after that?
There's a night mode plugin that puts a lightbulb in the menu bar at the top. I installed that. But, I also have some custom CSS that puts a box with radius corners around each category and topic. The color for that background is specified in the CSS, and doesn't change.
I'm guessing if I didn't have that custom CSS, things would work just fine. I wish there was an option in the persona theme to enable boxes around these things. Having everything on a white canvas with no separation looks messy to me, not minimal.
You can see it work at https://packetforum.com