If you want to target the SCLogin module buttons, you can add the class to the already existing styles in your template CSS if you want. You'll just add the classes to target the SCLogin buttons as well.
For example, looking at your page you have the "uk-button uk-button-primary" class. You can update the styles in your CSS like:
.uk-button.uk-button-primary { ... }to
.uk-button.uk-button-primary, .sclogin .btn.btn-primary { ... }
If you need more help with a specific style that's not working, please let me know.
-Melissa