This is not suppose to apply in revealjs

It is coming from styles-callout.html and it overriden by revealjs specific

Author: cderv

src/resources/formats/revealjs/quarto.scss

@@ -1006,12 +1006,9 @@ kbd {
     }
 
     .callout-icon::before {
-      height: 0.9em;
-      width: 0.9em;
       display: inline-block;
       content: "";
       background-repeat: no-repeat;
-      background-size: contain;
     }
 
     div {