What to run
Open Contrast Checker. It stays in the browser.
How to read the result
Ratio is relative luminance contrast.
AA for normal text is 4.5:1. AA for large text is 3:1. AAA is 7:1 and 4.5:1.
A pass for large text is not a pass for body text.
The check is the two colours, not the font rendering.
What to open next
Open Hex to RGB if you only have one form. It stays in the browser.
Do not use the favicon colours as the UI palette without re-checking.