Scale/zoom a DOM element and the space it occupies using CSS3 transform scale()

Question

In the middle of my page I have a div element with some content in it (other divs, images, whatever).

    before



        
      

Answer 1

The HTML (Thanks Rory)

  


  
  

    

      before
    
    
    

      
something inside
      

      
another something
    
    
    

      after
    
  
  

The CSS (Still started from Rory's base)

body {
  font-size: 13px;
  background-color: #fff;
}
#wrapper {
  width: 50%;
  margin-left: auto;
  margin-right: auto;
  border: 0.07692307692307693em solid #888;
  padding: 1.1538461538461537em;
}
.surrounding-content {
  border: 0.07692307692307693em solid #eee;
}
#content-to-scale {
  border: 0.07692307692307693em solid #bbb;
  width: 10em;
}
#content-to-scale {
  font-size: 1.1em;
}
#content-to-scale img {
  width: auto;
  height: auto;
  min-width: 100%;
  max-width: 100%;
}

The Explanation:

I'm using font size and ems to "scale" the dimensions of the child elements.

Ems are dimension units that are relative to the current context's font-size.

So if I say I have a font-size of 13px and a border of 1 (the desired border-width in pixels) divded by 13 (the current context's font-size also in pixels) = 0.07692307692307693em the browser ought to render a 1px border

To emulate a 15px padding I use the same formula, (desired pixels)/(current context's font-size in pixels) = desired ems. 15 / 13 = 1.1538461538461537em

To tame the scaling of the image I use an old favorite of mine: the natural ratio preserving scale, let me explain:

Images have a natural height and width and a ratio between them. Most browser's will preserve this ratio if both width and height are set to auto. You can then control the desired width with min-width and max-width, in this case making it always scale to the full width of the parent element, even when it will scale beyond it's natural width.

(You can also use max-width and max-height 100% to prevent the image from busting out of the borders of the parent element, but never scaling beyond their natural dimensions)

You can now control the scaling by tweaking the font-size on #content-to-scale. 1.1em roughly equals scale(1.1)

This does have some drawbacks: nested font-sizing in ems are applied recusively. Meaning if you have:

    
        
            Text
        
    

You will end up with "Text" rendering at 4px instead of the 8px you might expect.