Sometimes you only want to make some minor edits to a specific slider and you don't want to create a new custom skin just for a small edit. For this situation, you can add custom CSS to that slider.
Custom CSS panel
Custom CSS code window
When you add custom CSS code to a slider, a CSS file containing that code will be created in /plugins/slider-pro/custom/slider-pro-ID/slider-pro-ID-css.css, where 'ID' is the actual ID of the slider.
NOTE: In order to edit the skins or create custom skins, the 'skins' folder (/wp-content/plugins/slider-pro/skins/slider/) and the 'custom' folder (/wp-content/plugins/slider-pro/custom) need to be writable. On some servers this means that the folder has to have the permission set to 755, but on other servers it has to have the permission set to 777. I recommend checking with your web host what the best permission setting for making the folder writable would be.