Responsive css background images

Question

I have a website (g-floors.eu) and I want to make the background (in css I have defined a bg-image for the content) also responsive. Unfortunately I really don't have any idea on how to do this except for one thing that I can think of but it's quite a workaround. Creating multiple images and then using css screen size to change the images but I wanna know if there is a more practical way in order to achieve this.

Basically what I wanna achieve is that the image (with the watermark 'G') automatically resizes without displaying less of the image. If it's possible of course

link: g-floors.eu

Code I have so far (content part)

#content {
  background-image: url('../images/bg.png');
  background-repeat: no-repeat;
  position: relative;
  width: 85%;
  height: 610px;
  margin-left: auto;
  margin-right: auto;
}

Answer 1

If you want the same image to scale based on the size of the browser window:

background-image:url('../images/bg.png');
background-repeat:no-repeat;
background-size:contain;
background-position:center;

Do not set width, height, or margins.

EDIT: The previous line about not setting width, height or margin refers to OP's original question about scaling with the window size. In other use cases, you may want to set width/height/margins if necessary.