DevTools failed to load SourceMap: Could not load content for http://dev.styli.st/skin/frontend/mgstheme/ethan/css/main.css.map: code example

Example: DevTools failed to load SourceMap: Could not load content for

Open Developer Tools, 
go to "Settings" for Developer Tools, 
then uncheck Enable JavaScript Sourcemaps under the "Sources" settings.
Restart Browser if needed