Background-image getting a local resource picture

When you use Background-image to get a picture of a local resource, the following error occurs

The official documentation stated that local resources could not be obtained through WXSS, but could be used with network images, or base64 network images
http://www.moepan.net/
Upload the picture and then copy the outer link address to the URL base64
http://base64.xpcha.com/
Upload the picture, and then copy the transcoding to the URL (after transcoding is long, so I usually choose to use the network image)