Hi don't think I completely understand what you are trying, but the code below should help you add the arrow in your example above.
You can also find the code with a nice explanation here: https://www.ghostplugins.com/steps/go-arrow-button-style-version-2
Code:
// Go Arrow Button - Button Padding //
.sqs-block-button-element--medium
{
padding: 20px 30px !important;
border: 2px solid #000000 !important;
}
// Go Arrow Button - Arrow Icon Style //
.sqs-block-button-element--medium:after {
content: '➔';
color: #000000 !important;
border-left: 2px solid #000000;
padding-left: 30px;
margin: 0px 0px 0px 30px;
}