CSS和HTML_html/css_WEB-ITnose

I set up the picture to drop down on the web page and keep it fixed at a certain position on the monitor. But there is a shadow on Firefox, what's going on? How to solve it? Thank you for your help
The code is:
There is a white border on the picture effect.

Reply to discussion (solution)

margin: -1px -1 px,0px,0px;

It doesn’t seem to work

Set margin for the image and see. . Your button is absolutely positioned, so setting margin won't work.