revealjs - use rem units for spacing in columns

This is to be relative to base font size and not depend of element size for elements in column

This complements previous changes regarding spacing 805f7ad and d987a8c

closes #9999

Author: cderv

news/changelog-1.6.md

@@ -41,6 +41,7 @@ All changes included in 1.6:
 - ([#9558](https://github.com/quarto-dev/quarto-cli/issues/9558)): To prevent default footer to show on slide, set `footer='false'` attribute on the slide header, e.g. `## Slide with no footer {footer='false'}`
 - ([#6012](https://github.com/quarto-dev/quarto-cli/issues/6012)): Add styling for `kbd` element in Revealjs slides.
 - ([#10887](https://github.com/quarto-dev/quarto-cli/issues/10887)): Updating default Mathjax used from 2.7.0 to 2.7.9.
+- ([#9999](https://github.com/quarto-dev/quarto-cli/issues/9999)): Fix spacing problems of different size elements in columns.
 
 ## `typst` Format
 

src/resources/formats/revealjs/quarto.scss

@@ -461,17 +461,17 @@ $panel-sidebar-padding: 0.5em;
 }
 
 .reveal .columns > .column > :not(ul, ol) {
-  margin-left: 0.25em;
-  margin-right: 0.25em;
+  margin-left: 0.25rem;
+  margin-right: 0.25rem;
 }
 
 .reveal .columns > .column:first-child > :not(ul, ol) {
-  margin-right: 0.5em;
+  margin-right: 0.5rem;
   margin-left: 0;
 }
 .reveal .columns > .column:last-child > :not(ul, ol) {
   margin-right: 0;
-  margin-left: 0.5em;
+  margin-left: 0.5rem;
 }
 
 .reveal .slide-number {