I found the answer to my own question. May be of help to someone else….
In the Juiz Social plugin settings there are eight styles (at the time of writing). There are also eight css styles in the plugin folder. In my case, I use the second style on the list so in the WordPress Dashboard I went to Plugins > Editor > Juiz Social Post Sharer > css/juiz-social-post-sharer-2.min.css
To make the buttons smaller I changed
.juiz_sps_links .juiz_sps_item a{vertical-align:top;padding:5px 15px 5px 10px;
to
.juiz_sps_links .juiz_sps_item a{vertical-align:top;padding:1px 10px 1px 5px;
You can also change the button text colour and text size by editing
color:#646e76;text-decoration:none;font-size:12px;
Don’t forget that any changes will be overwritten when the plugin is updated but it’s easy to edit the css file again and really worth it because it’s a great lightweight social sharing plugin – the best I could find.
Feature request – Instagram would be great. ??
