After some mix-and-matching of the awesome code snippets posted in the comments, I came up with something easy on the eyes (with a nice little color transition (for webkit-enabled browsers):

data:text/html, <html><head><link href='http://fonts.googleapis.com/css?family=Lato:100,200,300,400,... rel='stylesheet' type='text/css'><style type="text/css"> html { font-family: "Lato"; color:#e9e9e9; background-color:#222; } * { -webkit-transition: all linear 1s; }</style></head><body contenteditable style="font-size:2.2em;line-height:1.4;max-width:60rem;margin:0 auto;padding:4rem;">