Your class definition of *spacer is invalid. * is a reserved character in CSS and cannot be used in class names. I removed it from my solution.
The spacer element had property display: block which makes it hard to size its content. Block elements inherently take the full width of the parent making it hard to assess the joint size of the image and filler text. I changed it to display: inline-block. Now we can easily figure out the amount of space to fill.
To track the size of one unit of the filler text I created a <span> around the word Wau. This allows me to accurately measure the size of this guy. Now I know how many times to repeat it in order to fill the space. JS has new calculations to run this thing.