That editor only has as many lines as there are content. There were only two lines of content there, so the editor is only two lines long. If you add some line breaks to the second line, for example, the editor gets bigger.
However, there's no good reason for that card to be an HTML card. I changed it to a Basic card, and it's all much more readable now.
Ethan McCutchen.....2018-03-28 11:25:22 UTC