The base for visual customization of the <SocialShare> buttons are the builtin CSS classes:
.social-share-button.social-share-button--{network name}.social-share-button--styled (only if styled is set to true).social-share-button__icon.social-share-button__labeland the CSS brand color variable, applied to the <a> element, and available to all its children:
--color-brandThe component CSS styles are placed inside a @layer components CSS layer.
Using a layer ensures a lower specicifity over regualar unlayered CSS, allowing for easy overwriting with your own customizations.
@layer rule for more info about this feature