keeping div boxes in the same place, i need some help Options

[rewop]

all my codes after a some amount of time alter so that all the boxes move up, to the left; or out of position. also it tends to look different on other people's computers.

could it be that i am defining positions with percents?

here's an example of one code

CODE

.div1 {
background-color:black; color:white;
border:2px solid; border-color:silver;
width:789px; height:1000px; overflow:inherit;
position:absolute; z-index:2; left:50%; top:0%;
margin-left:-394px; margin-top:150px; text-align:center;
visibility:visible;}
marquee { z-index:8; }

[rewop]

oh lol sorry..i just made something up as i went along..
i think i forgot i put the margin-left and 'top'. its just a habit..i usually use that in a code but i've been trying percents and therein lies my problem.