Merge pull request #18851 from ju1ius/patch-1

Don't clearfix if flexbox is enabled. Fixes #18849

diff --cc scss/_card.scss
index 01a5733d6af3e9332d141cc71d626c04b8f1aa71,646a2815826839553748ed879304b17da8d1dcb8..23a5e07c7225d91c1810eaabeead155337d15d54
--- 1/scss/_card.scss
--- 2/scss/_card.scss
+++ b/scss/_card.scss
@@@ -68,9 -71,10 +70,11 @@@
  //
  
  .card-header {
-   @include clearfix;
+   @if (not $enable-flex) {
+     @include clearfix;
+   }
    padding: $card-spacer-y $card-spacer-x;
 +  margin-bottom: 0; // Removes the default margin-bottom of <hN>
    background-color: $card-cap-bg;
    border-bottom: $card-border-width solid $card-border-color;