Small Button
<div class="sqs-block button-block sqs-block-button BlogList-item-excerpt"><div class="sqs-block-content">
<div class="sqs-block-button-container--center" data-alignment="center" data-button-size="small">
<a href="{permalink}" class="sqs-block-button-element--small sqs-block-button-element" data-initialized="true">Read More</a>
</div></div></div>
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Under Design > Style Editor > Blog: List > Read More Link, choose Hide to hide the default Read More link.
Navigate to Blog page.
Copy the code above and paste into Settings > Advanced > Post Blog Item Code Injection to get a Read More Link.
Notes:
The class "BlogList-item-excerpt" is used to keep the Read More link under the excerpt.
The other classes and data attributes were copied directly from the buttons in Brine (though should work with most templates).
Replace "small" with "medium" for medium buttons and "large" for large buttons.