Remark.js presentation change font size inside slide

.remark-slide-content {font-size: 40px;}

(from Font size · Issue #104 · gnab/remark · GitHub)

Also relevant are the content classes mentioned in how to adjust the font of a specific sentense/paragraph/word ? · Issue #230 · gnab/remark · GitHub:

Some text is .large[larger] and some is .small[smaller].

<style>
  .large { font-size: 130% } 
  .small { font-size: 70% }
</style>