无法在全屏模式下使图像元素全屏显示

I have a modal which takes the full width and height of a browser.In the modal there is an image within a div and some other elements,now I am trying to make the image full screen in the browser as like as a youtube video acts full screen, I have added a button and implemented full screen API in it for the purpose but it does not work.I have a modal which takes the full width and h