Customizing the Plugin CSS
If you want to modify the default styling included with the plugin, you can very easily do so in an upgrade-safe manner by copying the default CSS file to a specific folder inside of your theme, and then modifying the file to suit your needs.
First, create a folder inside of your theme called edd_templates, if it doesn’t already exist.
Second, copy the file from easydigitaldownloads/templates/edd.css to the new edd_templates directory.
Once you have done this, the plugin will load your custom version of the CSS, instead of the one provided by the plugin.