Close #2027. Fix usage of rgba() (#2028)

Changed to `rgb`

Author: databyte

src/plugins/clear_button/plugin.scss

@@ -7,7 +7,7 @@
         width: 25px;
         top: 0;
         right: calc(#{$select-padding-x} - #{$select-padding-item-x});
-        color: rgba(0, 0, 0);
+        color: rgb(0, 0, 0);
         opacity: 0.4;
         font-weight: bold;
         border: none;