RFR: 7299: Accessibility Issue - Too low contrast on rule result values

[Suchita Chaturvedi]

This PR addresses an accessibility issue where the contrast of the rules score on Automated Analysis screen is too low.

Please review the change and let me know if any changes are required.

The UI looks like this now:

![image](https://user-images.githubusercontent.com/11155712/122291146-1c887d00-cf12-11eb-957f-03f662f2805f.png)

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Commit messages:
 - 7299: Accessibility Issue - Too low contrast on rule result values

Changes: https://git.openjdk.java.net/jmc/pull/268/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=268&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-7299
  Stats: 4 lines in 1 file changed: 0 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/jmc/pull/268.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/268/head:pull/268

PR: https://git.openjdk.java.net/jmc/pull/268