Trying to hide the Share button with CSS

Product Support
3

Specifically which button? The one at the bottom of the topic?

If so, try this:

.topic-footer-main-buttons .btn-default.share {
    display: none;
}

.topic-footer-main-buttons .btn-default.invite-topic{
    display: none;
}

Also, please try and select a category when you make posts here on Meta.