alerta personalizado pero no funciona return confirm

[angel2010]

hola a todos tengo un problema ya pude decorar la ventana de alerta javascript
pero no se como colocar estylo a la ventana de confirm
voy a colocar el codigo para ver si me pueden ayudar

codigo javascript

Código Javascript:

// constants to define the title of the alert and button text.
var ALERT_TITLE = "cecilio acosta";
var ALERT_BUTTON_TEXT = "Ok";
 
// over-ride the alert method only if this a newer browser.
// Older browser will see standard alerts
if(document.getElementById) {
    window.alert = function(txt) {
        createCustomAlert(txt);
    }   
}
 
function createCustomAlert(txt) {
    // shortcut reference to the document object
    d = document;
 
    // if the modalContainer object already exists in the DOM, bail out.
    if(d.getElementById("modalContainer")) return;
 
    // create the modalContainer div as a child of the BODY element
    mObj = d.getElementsByTagName("body")[0].appendChild(d.createElement("div"));
    mObj.id = "modalContainer";
     // make sure its as tall as it needs to be to overlay all the content on the page
    mObj.style.height = document.documentElement.scrollHeight + "px";
 
    // create the DIV that will be the alert 
    alertObj = mObj.appendChild(d.createElement("div"));
    alertObj.id = "alertBox";
    // MSIE doesnt treat position:fixed correctly, so this compensates for positioning the alert
    if(d.all && !window.opera) alertObj.style.top = document.documentElement.scrollTop + "px";
    // center the alert box
    alertObj.style.left = (d.documentElement.scrollWidth - alertObj.offsetWidth)/2 + "px";
 
    // create an H1 element as the title bar
    h1 = alertObj.appendChild(d.createElement("h1"));
    h1.appendChild(d.createTextNode(ALERT_TITLE));
 
    // create a paragraph element to contain the txt argument
    msg = alertObj.appendChild(d.createElement("p"));
    msg.innerHTML = txt;
    
    // create an anchor element to use as the confirmation button.
    btn = alertObj.appendChild(d.createElement("a"));
    btn.id = "closeBtn";
    btn.appendChild(d.createTextNode(ALERT_BUTTON_TEXT));
    btn.href = "#";
    // set up the onclick event to remove the alert when the anchor is clicked
    btn.onclick = function() { removeCustomAlert();return false; }
 
    
}
 
// removes the custom alert from the DOM
function removeCustomAlert() {
    document.getElementsByTagName("body")[0].removeChild(document.getElementById("modalContainer"));
}
 

estylo de la ventana alerta

Código CSS:

#modalContainer {
    background-color:transparent;
    position:absolute;
    width:100%;
    height:100%;
    top:0px;
    left:0px;
    z-index:10000;
    background-image:url(fond.png); /* required by MSIE to prevent actions on lower z-index elements */
}
 
#alertBox {
    position:relative;
    width:300px;
    min-height:100px;
    margin-top:50px;
    border:2px solid #000;
    background-color:#F2F5F6;
    background-image:url(alerta.png);
    background-repeat:no-repeat;
    background-position:20px 30px;
}
 
#modalContainer > #alertBox {
    position:fixed;
}
 
/*fondo titulo*/
#alertBox h1 {
    margin:0;
    font:bold 0.9em verdana,arial;
    background-color:#009900;
    color:#FFF;
    border-bottom:1px solid #00CC00;
    padding:2px 0 2px 5px;
}
 
/*fondo titulo*/
#alertBox p {
    font:0.7em verdana,arial;
    height:50px;
    padding-left:5px;
    margin-left:55px;
}
 
/*booton*/
#alertBox #closeBtn {
    display:block;
    position:relative;
    margin:5px auto;
    padding:3px;
    border:1px solid #CCCCCC;
    width:70px;
    font:0.7em verdana,arial;
    text-transform:uppercase;
    text-align:center;
    color:#FFF;
    background-color:#00CCFF;
    text-decoration:none;
}
 

funciones del alerta
<input type = "button" value = "Prueba de la alerta" onclick = "alert ('. Se trata de un diálogo personalizado de alerta que fue creado por un exceso de montar el método window.alert'); "/>

quiero que funcione para onClick="return confirm