title: what makes this "aside" (in the body of the Q) be 100% height of body height?
body: <p>Sorry for the unclear title, 
  I just can't figure out exactly what I am asking..</p>
  
  <p>I am learning a lot by seeing the source and "inspecting elements" on any website.</p>
  
  <p>while doing so in  <a href="http://learn.shayhowe.com/html-css/adding-media/" rel="nofollow noreferrer">this site</a> (where I am learning HTML and CSS) I just failed to understand what makes the <code>&lt;aside&gt;</code> on the left have 100% height of the body.</p>
  
  <p>it has no rule for "height", and it's content is not big enough to make the div expand so much... (it's content covers maybe 10th of the total height..).</p>
  
  <p>to make it clear which part I am talking about, take a look at the following pictures:</p>
  
  <p>this pic is just to show you where in the doc to look for:
  <a href="https://i.stack.imgur.com/GwQ9V.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GwQ9V.png" alt="the source of the guilty aside"></a></p>
  
  <p>and this pic shows the aside in the rendered page (the aside goes all the way down to the bottom of the scroll... please see it in the <a href="http://learn.shayhowe.com/html-css/adding-media/" rel="nofollow noreferrer">site</a> to understand a little better :
  <a href="https://i.stack.imgur.com/OMikc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/OMikc.png" alt="enter image description here"></a></p>
  
  <p>hope you can help me figure it out :) </p>
  
  <p>Thanks a lot</p>