Hi! I’m just a user but it think this would help:
– Go to the plugins
– Select the Favorites plugin and click on Settings
– Go to Display & Post Types
– Go down to “Favorite Button Content & Appearance”
– Button HTML Element: Button
– Button Type: Custom
– Specify your custom colors
In the next two sections (Button Markup: Favorited / Button Markup: Unfavorited) you can use HTML/CSS.
My example for “Button Markup: Unfavorited”:
<span style=”font-size: 0.9375rem;display:block;width:115px;”><i class=”fas fa-thumbtack” style=”margin-right:10px;”></I>Add favorite</span>