A known problem if you are using percentage (or viewport unit) width and height for <body>
is that when mobile keyboard invoke due to input the size of any percentage/viewport element will change .
I've searched a lot about this problem and nothing could really help.
I found one of the answer is to adjust the layout according to the new viewport : mobile viewport resize due to keyboard
but this is not really practical.
Does anybody know how to manipulate mobile keyboard on web ?
After some test's I found a hack that i'll put in the answers, if there are better ways, please tell :)