The blockpage is just a htmlpage delivered to the client.
So if you want it to selfadjust according to windowsize you should create your html so it will do so.
The most simple way is just something like:
or perhaps just a blank page (but you must then inform the clients about this )
Click Accept as Solution to acknowledge that the answer to your question has been provided.
The button appears next to the replies on topics you’ve started. The member who gave the solution and all future visitors to this topic will appreciate it!
These simple actions take just seconds of your time, but go a long way in showing appreciation for community members and the LIVEcommunity as a whole!
The LIVEcommunity thanks you for your participation!