A couple of themes that I have put together for Discord. They should work either in your browser with the Stylish extension, with BeautifulDiscord, or with BetterDiscord. Feel free to use parts of my themes to create your own (please give credit if you do).
A theme that is styled to be as minimal as possible while still looking nice when the window size is small. It uses UndeadLeech's undead-discord theme to allow you to change the color of Discord to your liking just by a few hex colors in the root section of the theme. The guilds wrapper will be hidden to the left, and the channel and member list will be hidden to the right when the window width is below 1000px. After being hidden, both can be activated by hovering your mouse at the edge.
A theme that removes almost all elements of Discord other than Voice chat channels when the window is less than 700px wide. The majority of the voice channels will and users in them will remain visible regardless of size of Discord's window. The guild wrapper is hidden to the left side.
If you want the theme to be transparent, you will need BetterDiscord and the Transparency Patcher by HoLLy. After patching with the plugin, apply the theme in BetterDiscord's settings. After this, you will have to reload for the transparency to take effect. You will also have to refresh every time you restart Discord.
If you're on Windows, you can use the AutoHotkey script to make the Discord window be always on top and able to be clicked through. The default hotkey is `Ctrl+Space`
Included in this script is a hotkey to make windowed games run in a borderless window. The default hotkey is `Ctrl+Alt+Shift+Q`