Changed color for better color contrast ratio

[SaravgiYash]

Fixes #39

[mmaismma]

You have got two problems with your PR. Hence we can not accept it, please make another PR with the correct changes.

Problem 1

You have changed --themeColor in the correct file i.e. Source/cubfan135/style.css. But for the "Preview", you changed the color in the wrong file. As our contributing guidelines clearly states

Please commit all the changes in the beta version of the tool only. Beta version of anything is located under Source/ with the same rest of the location.

You had to change the CSS file located under Source/cubfan135/style.css.

Problem 2

Further, you had to make a PR to merge into Hermit-Tools:accessibility-improvements but you made the PR to merge into the master branch.
To make a PR merge into another branch select the branch just after you click on "New Pull Request".

Don't hesitate to contact me in case. Please make another PR with the correct changes.