CSS for plugin title 'Published Articles Since...'

I have the plugin "Published Articles Since Last Visit" and would like to change the title of what is show to 18 point font rather than H3.

I tried this in my CSS but it didn't change anything.

.norilsk {
font-size: 18px !important;
}

There are settings that can be changed inside Settings>Plugin, but I didn't see anything for font size.

I have given access through the DPMUDEV board. My site is restministries.com and this shows up on blog posts such as this:
http://restministries.com/2015/07/healthy-eating/

Thank you in advance.