When Using The Document.write, How Can I Position It And Apply CSS?

Here is my code:

function executeUntil(end)
{
var i=0 ;
while(i< 100)
{
if(i==end)
break ;
document.write("Javascript is fun");
i++;
}
return(i);
};
(executeUntil(01));

@ runtime, the output is Javascript is fun (obviously).

My question is, how can I apply a CSS style to the document.write output, and how can I make a layer (well I know how to do that, lol), but say that I want the output to appear in that layer to control the appearance of the content? If I can do the latter with the layer, then applying a CSS style is simple.