remove css leftover

ui/src/shared/mixins.css

@@ -1,30 +0,0 @@
-~boxes: "./constants.js";
-
-@define-mixin pseduo-element $type, $width:auto, $height:auto, $top:auto, $right:auto, $bottom:auto, $left:auto {
-  position: relative;
-
-  &:$( type ) {
-    bottom: $bottom;
-    content: "";
-    display: inline-block;
-    height: $height;
-    left: $left;
-    position: absolute;
-    right: $right;
-    top: $top;
-    width: $width;
-
-    @mixin-content;
-  }
-}
-
-@define-mixin move-z $amount:0, $position:relative {
-  position: $position;
-  z-index: $amount;
-}
-
-@define-mixin create-base-box-properties $border-radius: ~boxes.borderRadius, $border: ~boxes.border.unchecked, $box-shadow: ~boxes.bottomShaddow {
-  border: $border;
-  border-radius: $border-radius;
-  box-shadow: $box-shadow;
-}