Check if your Chrome is updated and the Rmarkdown package. It seems to be running fine for me.
Try these settings as I ran using these ones:
css: ['css/custom_resume.css', 'css/styles.css', 'resume']
# set it to true for a self-contained HTML page but it'll take longer to render
# uncomment this line to produce HTML and PDF in RStudio:
It doesnot open the browser but a pdf file