With Pro version, you can change Border in Style Settings > Read More.
With Free version, to change border (width, style, color) of Read More button, please use this CSS:
/* Change border of Read More button */
.pt-cv-view .pt-cv-readmore {
border-width: 3px !important;
border-style: solid !important;
border-color: red !important;
}
.pt-cv-view .pt-cv-readmore:hover {
border-width: 3px !important;
border-style: solid !important;
border-color: red !important;
}
You can change values of width, style, color as you want.
Best regards,