`.mark` and `.small` classes are also available to apply the same styles as `<mark>` and `<small>`whileavoidinganyunwantedsemanticimplicationsthatthetagswouldbring.
Whilenotshownabove,feelfreetouse`<b>` and `<i>` in HTML5. `<b>` is meant to highlight words or phrases without conveying additional importance while `<i>`ismostlyforvoice,technicalterms,etc.
Bootstrapv4.3shipswiththeoptiontoenableresponsivefontsizes,allowingtexttoscalemorenaturallyacrossdeviceandviewportsizes.<abbrtitle="Responsive font sizes">RFS</abbr>canbeenabledbychangingthe`$enable-responsive-font-sizes` Sass variable to `true`andrecompilingBootstrap.
Tosupport<abbrtitle="Responsive font sizes">RFS</abbr>,weuseaSassmixintoreplaceournormal`font-size` properties. Responsive font sizes will be compiled into `calc()` functions with a mix of `rem`andviewportunitstoenabletheresponsivescalingbehavior.Moreabout<abbrtitle="Responsive font sizes">RFS</abbr>anditsconfigurationcanbefoundonits[GitHubrepository](https://github.com/twbs/rfs).