Css defaults error

Hi I have tried to change the css in my ironwood.master build
When I change the colour of the text in the css file

lms-main-v1.css

which is located in

themes/A_theme/custom-theme/lms/static/css

No colour change occurs on the page.
When i recompile all assets

I am getting the following error



Any idea on how I can achieve my colour change?