title: Change font size of Canvas without knowing font family
body: <p>Is there a way to only change the font size of a canvas context without having to know/write the font family.</p>
  
  <pre><code> var ctx = document.getElementById("canvas").getContext("2d");
  
   ctx.font = '20px Arial'; //Need to speficy both size and family...     
  </code></pre>
  
  <p>Note:</p>
  
  <pre><code>ctx.fontSize = '12px'; //doesn't exist so won't work...
  ctx.style.fontSize = '20 px' //doesn't exist so won't work... 
                           //we are changing the ctx, not the canvas itself
  </code></pre>
  
  <p>Other note: I could do something like: detect where 'px' is, remove what's before 'px' and replace it by my font size. But I'd like something easier than that if possible.</p>