Guys, please, seriously, stop that. They don’t work on mobile or desktop devices when the window size is smaller than the area required to see the [X] Close button.
Whom ever came up with this, it is a bad idea. Stop it now. Before I get pissed off enough to write a web proxy that specifically filters out such stupidity, or purposefully renders that to an offscreen invisible layer which is forced to be non-modal.
Don’t force me to get into an arms race with you. It will not end well.