Hi @soulpearl
at the moment you need custom CSS to change the size and color of the button.
Future PRO versions will give you the possibility to customize colors and size without code, but the current version only gives you the possibility to add CSS classes to the button.
Usually, the button inherits the style of the theme. If this is not your case, it means your theme uses some CSS selectors that are not very common.
You can add the shortcode parameter button_class to give the same CSS class of your theme to the button.
Which theme are you using? Depending on the theme I can tell you have to add to the shortcode to inherit the button style from your theme.
Or would you like a different style from the theme?
Best regards
Jose