title: How to reuse (extend) bootstrap css classes in rails/sass
body: <p>I @import "boostrap" in core.scss file which also import other scss files (e.g.: _modals.css).</p>
  
  <p>In modals.css I want to extend some bootstrap classes:</p>
  
  <pre><code>.modal-container {
    @extend .row;
  }
  </code></pre>
  
  <p>And extend does not work as expected: </p>
  
  <blockquote>
    <p>WARNING on line 42 of
    ....../_modals.css.scss:
    ".row" failed to @extend ".row".   The selector ".row" was not found. 
    This will be an error in future releases of Sass.   Use "@extend .row
    !optional" if the extend should be able to fail.</p>
  </blockquote>
  
  <ul>
  <li><p>The only way I made it work is to @import "bootstrap" again in
  _modals.scss but this actually includes the whole bootsrap inside this file...</p>
  
  <p>The other solution is to move all definitions which extends css in
  core.css file - in this case - css in much less structured ...</p></li>
  </ul>
  
  <p>How should I do it properly?</p>