Inquiring minds want to know... how does one switch themes? 
if you root your phone you can use something like substratum (OMS) and download themes from the store and apply them, you can basically almost anything, i for my part want all things dark, beside that i like the colors more it uses less battery on amoled, oleds and super amoled displays, it depends a bit what kind of phone one is using but the posibilities are endless :-)
sinde i've been working for the industry before i retired i kept in touch and do all custom on my various phones, hence perhaps i can be of help should someone be interested.
BTW in google chrome one better checks desktop version to get best results for this site.
for root method i recommend magisk
of course, depending on the brand of a phone they have built in but limited theming that can be found in menus like:
- system UI (Tuner)
- themes
- etc.
i attached a few shots to give a very limited idea. the example device is in green+black, while one is in blue+black and any combination is possible.
should anyone be interested i recommend to visit xda developers website to learn how to get the most out of smartphones and tablets and there are equivalents for iOS. don't hesitate to ask while even though i use macs for 28 years i would only have all the answers for android OS since that's my platform of choice for smart devices.
https://forum.xda-developers.com/subscription.php?do=viewsubscription
