title: How to override Bootstrap mixin without modifying the actual source code?
body: <p>I'm using Bootstrap 4 and I would like to change default style of button hover and active states. Those can't be changed with variables because those are hard coded in Sass mixins. For example:</p>
  
  <pre><code>@mixin button-variant($color, $background, $border) {
    $active-background: darken($background, 10%);
    $active-border: darken($border, 12%);
    ...
  </code></pre>
  
  <p>In order to get the style I want, I need to change darken to lighten and then change percents. </p>
  
  <p>I could modify source code but it doesn't sound like a good solution for maintenance. I could also override those values with my custom css file included after Bootstrap but then I basically need to copy-paste whole button source from Bootstrap and modify it. Because there is lot of button variants, there will be lot of overrides which would be unnecessary in case of I can include changes to Bootstrap css.</p>
  
  <p>Best solution would be to override whole button-variant mixin in Bootstrap before compilation so that in compiled Bootstrap file there is only css I want. What would be the best way to do that?</p>