我通过JS上传图片。如何修改css?

EDIT: I realized that because I didn't give out the full-code (I wrote a lot since it was for a final project but I just had issue with this one tiny thing), my question was a bit confusing. The answers below are excellent but I realized that when I compiled the image data from the query, I assigned it a class so I just used that to edit, drawing from the answers below to resize the image. Thank you!EDIT: I realized that because I didn't give out