feat: add option to change opacity

I just found this app because I wanted an Apple like search on Windows and liking it so far. I'm a big fan of Electron and open source stuff. I would like to change the opacity of the main search box so it partially blends into the background. I've tried changing the background-color on both the main and background devtools like this:

I don't really understand what that is doing though. I am guessing that is not permanent because it's just modifying the source in the inspector? How do I make permanent changes? I'm guessing download the full source, make the change and rebuild? I wish there were instructions somewhere on how to do all of that.

• I am on the latest Cerebro.app version
• I have searched the issues of this repo and believe that this is not a duplicate

• OS version and name:
• Cerebro.app version:
• Relevant information from devtools (See above how to open it):

Issue