Oh okay - just to be sure - that one in the right-hand panel?
To remove backgrounds and borders from both the login page on the site and from the side panel ONLY, add this to mezzanine.css. If you want to add only one of them, remove the other from the CSS.
.form-actions, .panel-account {
background: none !important;
border: none !important;
}
For the right-hand panel CSS to work you need to do yet this one thing:
1. Open templates/includes/user_panel.html
2. Add panel-account to class="panel" so that it looks like class="panel panel-account"
3. SAve and then add aforementioned CSS and you're done! Refrest site to see if it works