I could not find a way to enable Full Control for the feature Add and Customize Pages in Site Permissions screen.
I am the administrator of the Site Collection and have created this site myself, but still I could not allow myself to allow this feature. When used Check Permissions screen, it is showing Deny status (as below):
My Admin setting for SharePoint has Custom Script enabled (as below image):
I am using SharePoint Online(Office365).
来源：https://stackoverflow.com/questions/51647702/sharepoint-online-office-365-how-to-set-allow-full-control-permission-for-a