When installing the JCE editor can show the following error:

Could not find the file '/templates/YourTemplate/css/template.css' in the template or templates/system folder

This error means that your template css file does not have a dedicated editor.
To resolve this problem just copy the file editor.css present in the folder Templates\System\css\ and place it on the [your template folder]\css, then select the configuration page by the voice Components JCE - JCE Administration and enter the following fields with values:
Use Template CSS = No
Custom CSS file = templates/$template/css/editor.css