The website weblup(dot)net/templates/template3 looks 100% correct on the computer thusfar. The overflow is hidden and you can't see the mobile menu bar or the pictures that slide in. But when opened on the phone you can scroll over, and see where the mobile menu is and where the next photo to come in is. I have no idea what could be causeing this but if you need to see the css for how I set my overflow here it is:

html{
    transform: translate3d(0,0,0);
    -webkit-transform: translate3d(0,0,0);
    font-family: 'Raleway', Arial;  
}
body{
    overflow: hidden !important;    
}

Try other browsers on the phone. I tend to find the stock browser to be buggy so I install Chrome and look again. You will find that trying to support all browsers a losing battle.

you have no height, therefore the propery should be ignored. If it is not, then the ones adhering to your markup are likely at fault, or "figuring out" what you meant.

Try adding height 100% to body, html and see if that fixes your problem.