Yes, full-width is hard to read, but somehow I have some sympathy for such simple html pages ;-)
Usually I use CTRL+Shift+I and add style="max-width:500px" to the body or push the window to the side of the screen to resized it to 50%.
Usually I use CTRL+Shift+I and add style="max-width:500px" to the body or push the window to the side of the screen to resized it to 50%.