How to auto align/resizing picture even when web browser is change spontaneously ? (Like Youtube Video)

Currently, there is no style adjustment in the class. So the picture shift depending on the web browser size. However, if I were to change size of my browser window the picture stay the same size until I hit refresh. I want to get that out of the way. Similarly, like youtube video (see the picture).

Autoresizing1 Autoresizing2