xaringan的官方文档里说了对局部字体大小的调整办法:
You can change the font size of single words, sentences or complete slides by defining two new classes in my-theme.css which change the font size relative to its default. Here, they are named .small and .large:
.large { font-size: 130% }
.small { font-size: 70% }
Simply enclose the text you want to change in your Presentation in .small[some text here] or .large[].
请问如果我想把默认的字体大小,也就说所有slide的字体都同时调整,该怎么设置?