Acessibility improve dashboard text contrast

[benamar19-b]

Description

Text in the dashboard page : Graph subheadings, titles in portfolio has poor colour contrast.
Contrast has less than 4.5:1 minimum required by WCAG
The text color changed to have a higher contrast with the background in small text

Addressed Issue

#1624

Additional Details

before :

After change :

Checklist

• I have read and understand the contributing guidelines
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[owasp-dt-bot]

✅ Snyk checks have passed. No issues have been found so far.

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✅	Open Source Security	0	0	0	0	0 issues

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