Hi Donald,
Thats a good question and yes there is CSS for exactly what you are looking for. You’d have to look up some examples to get exactly the look and feel of what you are looking for e.g. colors of the horizontal rule, thickness, width, you could even use CSS effects such as drop shadows.
To incorporate this into the style of the Events Calendar Plugin I’d suggest you read this tutorial here: https://theeventscalendar.com/support/documentation/events-calendar-themers-guide/#customizingstyles
You will need a working knowledge of CSS and how stylesheets works, and that article above gives you all the pointers to how this is setup with our plugin.
Hope this helps.