positionIt = function() {
if( document.getElementById ) {
// Get a reference to BoxId and measure its width.
var div0 = document.getElementById( "Bkg" );
var div0Width = div0.offsetWidth ? div0.offsetWidth : div0.style.width ? parseInt( div0.style.width ) : 0;

// Calculating MarginX so the BoxId will be centered in the viewport.
var WidthT = div0Width;								/*Body_Width = Element_Gauche + Element_Droite*/
var MarginX = ( getViewportWidth() - WidthT ) / 2;		/*Margin_Body = (Viewport_Width - Body_Width) divisé par 2*/

// If MarginXhave become smaller than 0, make them 0.
if( MarginX < 0 ) MarginX = 0;

// Position the BoxId in the center of the page and make it visible.
div0.style.left = MarginX + "px";
}
}

getViewportWidth = function() {
var width = 0;
if( document.documentElement && document.documentElement.clientWidth ) {
width = document.documentElement.clientWidth;
}
else if( document.body && document.body.clientWidth ) {
width = document.body.clientWidth;
}
else if( window.innerWidth ) {
width = window.innerWidth - 18;
}
return width;
};

getViewportHeight = function() {
var height = 0;
if( document.documentElement && document.documentElement.clientHeight ) {
height = document.documentElement.clientHeight;
}
else if( document.body && document.body.clientHeight ) {
height = document.body.clientHeight;
}
else if( window.innerHeight ) {
height = window.innerHeight - 18;
}
return height;
};

window.onload = positionIt;
window.onresize = positionIt;