The editor of .Maui Pastebin is based on CodeMirror, you can see a preview of the themes here:
https://codemirror.net/demo/theme.html

The values accepted by our APIs to create a paste with a specific theme are:

default
3024-day
3024-night
abcdef
ambiance
base16-dark
base16-light
bespin
blackboard
cobalt
colorforth
darcula
dracula
duotone-dark
duotone-light
eclipse
elegant
erlang-dark
gruvbox-dark
hopscotch
icecoder
idea
isotope
lesser-dark
liquibyte
lucario
material
mbo
mdn-like
midnight
monokai
neat
neo
night
oceanic-next
panda-syntax
paraiso-dark
paraiso-light
pastel-on-dark
railscasts
rubyblue
seti
shadowfox
solarizeddark
solarizedlight
the-matrix
tomorrow-night-bright
tomorrow-night-eighties
ttcn
twilight
vibrant-ink
xq-dark
xq-light
yeti
zenburn