Hello Everyone,
If anyone is interested in doing this for me what worked is the following.
For instance I just selected the Text Block AddOn then selected the Style Tab. In the Custom CSS section at the bottom I added the following and it works. I did not need a CSS Class to make this work either.
.sppb-addon-text-block .sppb-addon-content {
border-left: 3px solid #12284C !important;
padding-left: 15px;
}
In the future if Joomshaper wishes to add a feature under Style for each AddOn that allowed someone to do this with a UI it could be done. But for now this works.
I believe Quix has this ability however the support from Quix hasn't been great which is why I switched to SP Page Builder Pro. No tool is perfect however the support from Joomshaper has been the best so far with my Joomla projects.
Enjoy!