Two columns with variable width and a fixed gap between them

Question

I need to style two columns dynamically. They should have a width of 50% each, but a fixed gap of 10px between them.

When I collapse my menu the columns should widen to

Answer 1

I know this is a few months old, but I have another potential solution, which I will post here for posterity, in case it helps someone else:

What I did was snug two columns right in next to each other, and then place the real columns inside of those columns, using a 5px margin on each, on the shared side, to create the illusion of a 10px gap.

I have set up a demo similar to the original one Chris put up, only using this trick to create the gap between the columns.

Here is a fiddle of the snippet below:

$(document).ready(function() {
  $('#left').click(function() {
    $('#left').text('').animate({
      width: '0%'
    }, 'slow');
    $('#right').animate({
      width: '98%'
    }, 'slow');
  });
});

#container {
  height: 500px;
  width: 90%
}
#left,
#right {
  border: 1px Red solid;
  height: 100%;
  width: 48%;
  float: left;
}
.halfWidthColumn {
  float: left;
  height: 100%;
  width: 50%;
  margin: 0px;
  padding: 0px;
}
.interiorColumn {
  border: 1px Black solid;
  background-color: White;
  height: 100%;
}
.leftSide {
  margin: 0 5px 0 0;
  background-color: Blue;
}
.rightSide {
  margin: 0 0 0 5px;
  background-color: Green;
}

  

    Click to collapse
  
  

    

      

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Notice that I am no longer using JavaScript to resize the two interior columns. I believe this will do what was originally requested, if I am not mistaken.