by default theme will be system's theme

[rohanjadhav05]

Fixes #3061

Changes:

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123

[raclim]

Thanks for your work on this! I think while this would work, I would like to find a solution that utilizes the suggested method in the issue, which is using the CSS media feature, prefers-color-scheme. Due to the amount of PRs we have open at the moment I'm going to close this one for now. I'm sorry that we couldn't get this one in, but please feel free to reopen this one with any updates or check out our other issues!