Changing the Editor Theme doesn't change the Python Editor theme

[lresende]

When using the Setting's menu to change the theme for the Text Editor it does not apply to the Python Editor.

[lresende]

author: @ajbozarth
The theme seems to be handled by codeeditor not fileeditor so there may be other functionality missing that is also handled in the same location. This should be investigated alongside this issue.

[kinow]

The python editor seems to be working fine for me when I switched to dark mode.

And also switching to the default theme and increasing font size.

[ajbozarth]

Thanks for checking into this, it seems some of our recent work has made some of the codeditor features like dark theme start working without realizing it.

[ajbozarth]

Though python editor seems to work ok, other parts of elyra don't support dark mode. I'm going to use this issue to track addressing elyra dark mode over all. I plan to work on this myself, but if a new dev would like to take it if before I get to it that's ok as well. I'll make sure to post here when I actually start work on this. Afaik the side bar icons and side bar widgets all need to be updated for dark mode support, as well as pipeline editor.

[ajbozarth]

Since #595 addresses the original intent of this PR, that is that code mirror functionality was missing. I opened #625 to handle general dark mode support