if using the default theme its
.wppizza-article-default .wppizza-article-size:after
if using the grid theme its
.wppizza-article-grid .wppizza-article-size:after
etc (reason being that you will be able to have different layouts for different pages if you want)
there is a min css (wppizza.css) that applies to all and selective overrides depending on layout used
if you want to overwrite things, copy custom.css as outlined earlier somewhere i believe to your child theme and overwrite it as needs be (or use your theme’s inline css option)