There are two files included in the CSS folder with .map file extensions. They are:
bootstrap-theme.css.map
bootstrap.css.map
They appear to be minified files but I don't know what they are for.
This question is related to
twitter-bootstrap-3
source-maps
What is a CSS map file?
It is a JSON format file that links the CSS file to its source files, normally, files written in preprocessors (i.e., Less, Sass, Stylus, etc.), this is in order do a live debug to the source files from the web browser.
What is CSS preprocessor? Examples: Sass, Less, Stylus
It is a CSS generator tool that uses programming power to generate CSS robustly and quickly.
Map files (source maps) are there to de-reference minified code (css and javascript).
And they are mainly used to help developers debugging a production environment, because developers usually use minified files for production which makes it impossible to debug. Map files help them de-referencing the code to see how the original file looked like.
Have you ever found yourself wishing you could keep your client-side code readable and more importantly debuggable even after you've combined and minified it, without impacting performance? Well now you can through the magic of source maps.
This article explains Source Maps using a practical approach.
The bootstrap css can be generated by Less. The main purpose of map file is used to link the css source code to less source code in the chrome dev tool. As we used to do .If we inspect the element in the chrome dev tool. you can see the source code of css. But if include the map file in the page with bootstrap css file. you can see the less code which apply to the element style you want to inspect.
If you just want to get rid of the error, you can also delete this line in bootstrap.css:
/*# sourceMappingURL=bootstrap.css.map */
For anyone who came here looking for these files (Like me), you can usually find them by adding .map to the end of the URL:
https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css.map
Be sure to replace the version with whatever version of Bootstrap you're using.
These are source maps. Provide these alongside compressed source files; developer tools such as those in Firefox and Chrome will use them to allow debugging as if the code was not compressed.
Source: Stackoverflow.com