Why does my browser import css rules from non-existent .less files when I include bootstrap.css

Question

The only thing I included is

<link href="bootstrap/css/bootstrap.css" rel="stylesheet" type="text/css">

When I view the webpage in chrome development tool > styles, there are many css rules included from files

bootstrap/css/less/mixins/vendor-prefixes.less
bootstrap/css/less/normalize.less
bootstrap/css/less/scaffolding.less

But there is no such files in my file system, and I am unable to find these filenames in bootstrap.css .

Answer 1

The Developer Tool is probabely reading the CSS Map by Bootstrap.

1) You can remove this map, bootstrap.css.map from your resources

2) You can disable it in the tool, Settings -> Sources -> Enable CSS source maps

Here is an introduction guide to source maps.