samsung galaxy position fixed popup window positioning

I am using disqus commenting system on a site. I disabled the mobile theme for the commenting in order to use our own version even on mobiles and ipad devices. Problem is that now the login popup window is not fixed to the middle of the window on ipad, samsung galaxy devices. It ends u开发者_Python百科p at the top of the page - out of site. I tried this css but it doesn't work on these devices only on desktop browswers.

#dsq-popup-message {
    position:fixed!important;
    top: 20%!important;
        left: 30%!important;
    bottom: 0!important;
} 

thanks for the help

position:fixed;

is not supported in mobile safari Fixed positioning in Mobile Safari