Added highlighting to active category

Description

Added highlighting for active category in sidebar

Closes #174

Add styling to router-link-active class

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[x] My submission is formatted according to the guidelines in the contributing guide
[x] My addition is ordered alphabetically
[x] My submission has a useful description
[x] Code follows the established CODE_OF_CONDUCT guidelines.
[x] Code has been tested thoroughly and passes all tests.
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[x] Pull request title follows the established pull request title format.
[x] Pull request description clearly describes the changes included in the pull request.
[x] The description does not have more than 100 characters
[x] Each table column is padded with one space on either side
[x] I have searched the repository for any relevant issues or pull requests
[x] Any category I am creating has the minimum requirement of 3 items