My css file :
enter image description here

And this file when build : ( not change )
enter image description here

Sometime I try "clean-solution" and "build-solution" then it’s working, but now isn’t working.
Thank.

>Solution :

May be the CSS file is cached. You can try open the Chrome Dev Tools -> Network tab -> tick the Disable cache checkbox and then F5 to refresh the page. Or just Ctrl+F5 to refresh with no cache.