This should solve your problem: FB Share button/dialog documentation Genereally speaking you can use either normal HTML code and style it with CSS, or you can use Javascript.
Here is an example:
<a href="https://www.facebook.com/sharer/sharer.php?u=https%3A%2F%2Fparse.com" target="_blank" rel="noopener">
<img class="YOUR_FB_CSS_STYLING_CLASS" src="img/YOUR_FB_ICON_IMAGE.png" width="22px" height="22px" alt="Share on Facebook">
</a>
Replace https%3A%2F%2Fparse.com, YOUR_FB_CSS_STYLING_CLASS and YOUR_FB_ICON_IMAGE.png with your own choices and you should be ok.
Note: For the sake of your users' security use the HTTPS link to FB, like in the a's href attribute.