You can theme your Discord app by using an application called Aliucord. Aliucord is a Discord client modification that works on Android. You can add almost do everything that BetterDiscord does but on mobile. You can add themes and you can also add plugins (if you didn't know).
Aliucord is against Discord's TOS! Please use Aliucord at your own risk!
LINKS
Aliucord Download
https://github.com/Aliucord/Aliucord/...
Aliucord Server (for plugin downloads)
/ discord
SOCIALS
Discord Server
/ discord
TIMESTAMPS
00:00 Intro
00:21 Installing Aliucord
01:57 Getting Themes
04:27 Uninstall