image preview has issues with large image and extension

[NewUserHa]

1. a large image like 1125*380 can see only the left half in the preview window on 2k/4k mobile device
2. a full-text content image like 425*960 size is unable to see the content in the preview window at all. besides, there's no resize function in it. hope the preview can work like an overlay full window with a close button as common behavior
3. the preview window should obey the Content-Type in headers to determine if an image instead of the url