fix: use is-dark for highlight dark theme

[DersJ]

Description

Applying change from 4.x.x branch

Test Steps

• [ ] npm run start
• [ ] then this
• [ ] finally this

General Tests for Every PR

• [ ] npm run start still works.
• [ ] npm run lint passes.
• [ ] npm run stylelint passes.
• [ ] npm test passes and code coverage is not lower.
• [ ] npm run build still works.

Screenshots or link to StackBlitz/Plunker

[owilliams320]

:tada: This PR is included in version 7.3.0 :tada:

The release is available on:

• v7.3.0
• GitHub release

Your semantic-release bot :package::rocket: