Theme Rigid-Light - How do I change the font colors?

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Hello. I have been using the theme, Rigid-Light. I am not able to change the font colors. I have tried all the normal ways,including inside each block and on the "customize" page of the theme. I went to the "I got style" css, but did not know how to use that info to change the font colors.

Thanks for your time and help. Have a wonderful day!

tamarosher