Using CSS to Add A Reading Progress Bar To My Site

The length of my posts can vary dramatically - some (like this one) are very short, whilst others are much, much longer. Although I generally try to indicate how long a post is, once a reader is in, there isn't really a good way to know how much more of the post is left (the days of thick scrollbars are, thankfully, quite some way behind us). So, I decided to add a small visual indicator - a coloured bar which creeps across the top of the page as you progress. Most functionality on my site wo...