Why 31000? Browsers accept 2147483648, so there's plenty of chance to get above the overlay if REALLY wanted.
This overlay only appears when the user is moving the mouse around during a drag operation (hand tool), and disappears when the mouse is released. Its sole purpose is to stay above all elements and force the mouse to be a "grabbing" cursor.

To prevent external styles from affecting this element, I've declared the styles as inline, to get CSS specifity 1,0,0,0. The alternative way to ensure no CSS conflicts is to declare the properties in a stylesheet, flagged `!important` (this option seems worse to me).