Hello @jabedoya60,
Thanks for asking. 
I think you are referring to Maps error in builder preview section. It’s a known bug and our developers are working to release a fix for the same in next release of X and Cornerstone. We are in beta testing phase and the final release should be available in next few weeks.
If you are referring to increase the font size of breadcrumbs, please add following CSS under X > Theme Options > CSS:
.x-breadcrumb-wrap {
font-size: 16px;
}
If you would like to learn CSS, I am sharing few resources that you take a look to get started with CSS and an interesting tool that you can use to speed up the development process.
I recommend you to watch following video that will help you to get started with CSS.
https://www.youtube.com/watch?v=MFR4WXiLzpc
Sometimes it can get a bit difficult to find out the right selector to be able to write the required CSS codes. A handy tool that can help you in this is Google Chrome dev tools. I am sharing the resource that you can refer to get started with dev tools.
https://developers.google.com/web/tools/chrome-devtools/
https://www.youtube.com/watch?v=tP_kXBJWPhQ&t=200s
Thanks.