fix: adding back side-nav style fix that was deleted during merge

[hectordavis]

Closes #

Summary
Adding back the fix introduced by this PR to prevent white theme from being applied to current page buttons in side nav.

Change List (commits, features, bugs, etc)
Fix added back in _side-nav.scss

Things to look for during review

• Make sure all references to iot or bx class prefix is using the prefix variable
• (React) All major areas have a data-testid attribute. New test ids should have test written to ensure they are not changed or removed.
• UI should be checked in RTL mode to ensure the proper handling of layout and text.
• All strings should be translatable.
• The code should pass a11y scans (The storybook a11y knob should show no violations). New components should have a11y test written.
• Unit test should be written and should have a coverage of 90% or higher in all areas.
• All components should be passing visual regression test. For new styles or components either a visual regression test should be written for all permutations or the base image updated.
• Changes or new components should either write new or update existing documentation.
• PR should link and close out an existing issue

[netlify]

✅ Deploy Preview for carbon-addons-iot-react ready!

Name	Link
🔨 Latest commit	a61bf3e
🔍 Latest deploy log	https://app.netlify.com/sites/carbon-addons-iot-react/deploys/6706b72fe202d800083d82d4
😎 Deploy Preview	https://deploy-preview-3889--carbon-addons-iot-react.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[herleraja]

LGTM