<input type="button" value = "Test the alert" onclick="alert('Alert this pages');" />
#modalContainer {
	background-color:rgba(0, 0, 0, 0.3);
	position:absolute;
  top:0;
	width:100%;
	height:100%;
	left:0px;
	z-index:10000;
	background-image:url(tp.png); /* required by MSIE to prevent actions on lower z-index elements */
}

#alertBox {
	position:relative;
	width:33%;
	min-height:100px;
  max-height:400px;
	margin-top:50px;
	border:1px solid #fff;
	background-color:#fff;
	background-repeat:no-repeat;
  top:30%;
}

#modalContainer > #alertBox {
	position:fixed;
}

#alertBox h1 {
	margin:0;
	font:bold 1em Raleway,arial;
	background-color:#f97352;
	color:#FFF;
	border-bottom:1px solid #f97352;
	padding:10px 0 10px 5px;
}

#alertBox p {
	height:50px;
	padding-left:5px;
  padding-top:30px;
  text-align:center;
  vertical-align:middle;
}

#alertBox #closeBtn {
	display:block;
	position:relative;
	margin:10px auto 10px auto;
	padding:7px;
	border:0 none;
	width:70px;
	text-transform:uppercase;
	text-align:center;
	color:#FFF;
	background-color:#f97352;
	border-radius: 0px;
	text-decoration:none;
  outline:0!important;
}

/* unrelated styles */

#mContainer {
	position:relative;
	width:600px;
	margin:auto;
	padding:5px;
	border-top:2px solid #fff;
	border-bottom:2px solid #fff;
}

h1,h2 {
	margin:0;
	padding:4px;
}

code {
	font-size:1.2em;
	color:#069;
}

#credits {
	position:relative;
	margin:25px auto 0px auto;
	width:350px; 
	font:0.7em verdana;
	border-top:1px solid #000;
	border-bottom:1px solid #000;
	height:90px;
	padding-top:4px;
}

#credits img {
	float:left;
	margin:5px 10px 5px 0px;
	border:1px solid #000000;
	width:80px;
	height:79px;
}

.important {
	background-color:#F5FCC8;
	padding:2px;

}

@media (max-width: 600px) 
{
  #alertBox {
	position:relative;
	width:90%;
  top:30%;
}
var ALERT_TITLE = "Oops!";
var ALERT_BUTTON_TEXT = "Ok";

if(document.getElementById) {
	window.alert = function(txt) {
		createCustomAlert(txt);
	}
}

function createCustomAlert(txt) {
	d = document;

	if(d.getElementById("modalContainer")) return;

	mObj = d.getElementsByTagName("body")[0].appendChild(d.createElement("div"));
	mObj.id = "modalContainer";
	mObj.style.height = d.documentElement.scrollHeight + "px";
	
	alertObj = mObj.appendChild(d.createElement("div"));
	alertObj.id = "alertBox";
	if(d.all && !window.opera) alertObj.style.top = document.documentElement.scrollTop + "px";
	alertObj.style.left = (d.documentElement.scrollWidth - alertObj.offsetWidth)/2 + "px";
	alertObj.style.visiblity="visible";

	h1 = alertObj.appendChild(d.createElement("h1"));
	h1.appendChild(d.createTextNode(ALERT_TITLE));

	msg = alertObj.appendChild(d.createElement("p"));
	//msg.appendChild(d.createTextNode(txt));
	msg.innerHTML = txt;

	btn = alertObj.appendChild(d.createElement("a"));
	btn.id = "closeBtn";
	btn.appendChild(d.createTextNode(ALERT_BUTTON_TEXT));
	btn.href = "#";
	btn.focus();
	btn.onclick = function() { removeCustomAlert();return false; }

	alertObj.style.display = "block";
	
}

function removeCustomAlert() {
	document.getElementsByTagName("body")[0].removeChild(document.getElementById("modalContainer"));
}
function ful(){
alert('Alert this pages');
}

External CSS

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External JavaScript

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