Do you use Web Compiler extension?

You can use Visual Studio's Web Compiler extension to create a bundle.css and test if CSS was compiled successfully. More information and download at Visual Studio Marketplace.

✅ Figure: Web Compiler can find missing curly braces

Unfortunately different kinds of errors, like are not caught.

❌ Figure: Curly braces in the wrong place, but still compiled successfully

In addition, Gulp is wrongly successful too:

❌ Figure: Gulp couldn't find the curly braces error