Set div to have its siblings width

Answer 1

UPDATE: This works with me, I've just tried it:

   

     
If you use 100% here, it will fit to the width of the mother div automatically.
     
 The div will be 100% of the mother div too.
   
     

Is this what you want? The borders and background are just to show the divs ;)

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Just go like this:

Let's say you want the whole divs be max. 980px (otherwise just leave that out or replace with 100%)...

     
If you use 100% here, it will fit to the width of the mother div automatically.
     
     
 The div will be 100% of the mother div too.
     

The second option would be, to use one more div... or you use style="width:auto;" for the dynamic div...