Resizing and scaling image in proportion when browser resizes
 

Hi,

I am having trouble with re sizing an image. I want the image to be the same proportion when the browser resizes, same width to height proportion. I tried some code but that messed up the images so only a part of the images show in the slideshow on the website I'm making: Northwestern University Materials Research Center | MR SEC. When I minimize the browser, the images in the slideshow get bigger on the page, but I want it so that the images are full size no matter the browser window size and they are always the same proportion and scaled.

How can I do that? I am using word press, and I can edit the custom CSS and html