Where to Change the Color of "Read More" in Lucid?
Design and Skin Customization
The class .blog-index-text is what controls the yellow border, you may need to look under the non tagged section of your Style tab to find it.
The button is the .blog-index-read-more class.
Alternatively, I think you can find these in your skins/jrLucid/css/index.css file, modify them to suit your needs, and then upload the file to your server via FTP.
Hope this helps!