Making bold and italics work in Slidify

Last week I gave a talk on how to make R packages (see my previous post). Given the topic, I though it would be quite appropriate to actually make my slides using an R package!

After considering the options, I decided on Slidify. This is essentially a nifty wrapper to other libraries and HTML presentation frameworks. Its default framework, io2012, looked great so I stuck with it.

Making the slides was quick and easy: I wrote my content in R Markdown and ran slidify() to compile it into a slick web-based slide deck. It was particularly simple to include R code and have it presented with nice syntax highlighting, as well as show the output of R commands (including plots!).

Although Slidify is relatively mature, there were a few wrinkles that I needed to iron out before I was happy with my slides. One of these was that emphasised text (bold and italics) didn’t display properly using io2012. This is actually a known, long-standing bug, but has an easy workaround. You simply need to define the following CSS styles:

em {
    font-style: italic
strong {
    font-weight: bold;

You could embed these rules inside your R Markdown code if you like (by wrapping them inside <style>...</style>), but I prefer to add them as a separate file. Slidify makes this straightforward: just create a CSS file inside assets/css with the above rules and it will automatically be included when you compile your slides (in your header make sure you set the mode page property to selfcontained, which is its default value).

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