title: Minifying Bootstrap css with BundleConfig
body: <p>I am working with ASP.NET MVC Framework 5 with BundleConfig, which allows me to bundle and minify my <code>.js</code> and <code>.css</code> files. Suddenly, I have realized that it can't minify Bootstrap <code>.css</code> files due to variables in it (version 4.3.1). I always see such errors:</p>
  <pre><code>/* Minification failed. Returning unminified contents.
  (1,39): run-time error CSS1062: Expected semicolon or closing curly-brace, found '-'
  (1,56): run-time error CSS1062: Expected semicolon or closing curly-brace, found '-'    
  </code></pre>
  <p>I have tried using SCSS minified files and pure CSS provided by Bootstrap, but in all cases result is the same. SCSS files can be minified by web compiler, but BundleConfig is still trying to compress them by itself and fails. Even with the single file.</p>
  <pre><code>    public static void RegisterBundles(BundleCollection bundles)
      {
          bundles.Add(new StyleBundle(&quot;~/Content/css&quot;).Include(
                    &quot;~/Content/bootstrap.min.css&quot;));
      }
  </code></pre>
  <p>In addition, I have used different minifiers and found out that they give different results for the same file and it is hard to understand which is better.</p>
  <p>But even if I would use any external tool, I need advice on what should I do with my BundleConfig not to show these errors.</p>