How the alert style for JS changes as background color _javascript tips

Copy Code code as follows:

Window.alert = function (str)
{
var shield = document.createelement ("DIV");
Shield.id = "shield";
Shield.style.position = "absolute";
Shield.style.left = "0px";
Shield.style.top = "0px";
Shield.style.width = "100%";
Shield.style.height = document.body.scrollheight+ "px";
Background color when a dialog box pops up
Shield.style.background = "#fff";
shield.style.textAlign = "center";
Shield.style.zIndex = "25";
Background transparent IE effective
Shield.style.filter = "Alpha (opacity=0)";
var Alertfram = document.createelement ("DIV");
Alertfram.id= "Alertfram";
AlertFram.style.position = "absolute";
AlertFram.style.left = "50%";
AlertFram.style.top = "50%";
AlertFram.style.marginLeft = " -225px";
AlertFram.style.marginTop = " -75px";
AlertFram.style.width = "450px";
AlertFram.style.height = "150px";
AlertFram.style.background = "#ff0000";
alertFram.style.textAlign = "center";
AlertFram.style.lineHeight = "150px";
AlertFram.style.zIndex = "300";
strhtml = "<ul style=\" list-style:none;margin:0px;padding:0px;width:100%\ ">\n";
strHTML + = "<li style=\" background: #DD828D; text-align:left;padding-left:20px;font-size:14px;font-weight:bold; height:25px;line-height:25px;border:1px solid #F9CADE; \ ">[custom hint]</li>\n";
strHTML + = "<li style=\" background: #fff; text-align:center;font-size:12px;height:120px;line-height:120px; BORDER-LEFT:1PX solid #F9CADE border-right:1px solid #F9CADE; ">" +str+ "</li>\n";
strHTML + = "<li style=\" background: #FDEEF4; text-align:center;font-weight:bold;height:25px;line-height:25px; border:1px solid #F9CADE; \ "><input type=\" button\ "value=\" OK \ "Onclick=\" Dook () \ "/></li>\n";
strHTML + = "</ul>\n";
alertfram.innerhtml = strhtml;
Document.body.appendChild (Alertfram);
Document.body.appendChild (shield);
var ad = SetInterval ("Doalpha ()", 5);
This.dook = function () {
AlertFram.style.display = "None";
Shield.style.display = "None";
}
Alertfram.focus ();
Document.body.onselectstart = function () {return false;};
}

Effect as shown