Create enum for theme types

[Sakshee Jain]

I'm submitting a ...

• bug report
• feature request

Current behavior:

Currently we are not using enum for any them type, which makes the theme type less configurable. And whenever we need to use theme types somewhere, we would need to write explicitly.

Expected behavior:

There should be a common enum for all the theme types at one place, and it should be used everywhere. If someone changes at one place, it will automatically replace its all instances. This could also be done for other types.

Screenshots of the issue:

Will work on the issue:
Yes