A CodePen by Matt Boldt. CSS3 & jQuery Calculator - Now fully functional! Saw this graphic posted on Forrst and decided to code it.

index.html

<div class="wrap">
<div class="cal">
  <ul class="ctrls">
  	<li class="close"><a href="#"></a></li>
		<li class="min"><a href="#"></a></li>
		<li class="max"><a href="#"></a></li>
	</ul>
	<span class="title">Calculator</span>
	<div class="screen">2+2</div>
	<input type="hidden" class="outcome" value="2+2" />
	<ul class="buttons">
		<li><a class="clear">C</a></li>
		<li><a class="val" href="-">&plusmn;</a></li>
		<li><a class="val" href="/">&divide;</a></li>
		<li><a class="val" href="*">&times;</a></li>
		<li><a class="val" href="7">7</a></li>
		<li><a class="val" href="8">8</a></li>
		<li><a class="val" href="9">9</a></li>
		<li><a class="val" href="-">-</a></li>
		<li><a class="val" href="4">4</a></li>
		<li><a class="val" href="5">5</a></li>
		<li><a class="val" href="6">6</a></li>
		<li><a class="val" href="+">+</a></li>
		<li><a class="val" href="1">1</a></li>
		<li><a class="val" href="2">2</a></li>
		<li><a class="val" href="3">3</a></li>
		<li><a class="equal tall">=</a></li>
		<li><a class="val wide shift" href="0">0</a></li>
		<li><a class="val shift" href=".">.</a></li>
	</ul>
</div>




<p>I saw <a href="http://forrst.com/posts/Dark_Calculator_Mac_App-aff">this post</a> on <a href="http://forrst.com">Forrst</a> and figured I would give it a go!</a> 
  Follow me on <a href="http://www.twitter.com/atmattb">Twitter</a>, and let me know what you think. <a href="http://mattboldt.com/demos/calculator/">Original Source</a></p>

</div>

script.js

$(function(){

  // when a value is clicked
  $(".val").click(function(e){
    // prevent the link from acting like a link
    e.preventDefault();
    //grab this link's href value
  	var a = $(this).attr("href");
    // append said value to the screen
		$(".screen").append(a);
    // append same value to a hidden input
		$(".outcome").val($(".outcome").val() + a);
		
	});
  // when equals is clicked
	$(".equal").click(function(){
    // solve equation and put in hidden field
		$(".outcome").val(eval($(".outcome").val()));
    // take hidden field's value & put it on screen
		$(".screen").html(eval($(".outcome").val()));
	});
  // clear field
	$(".clear").click(function(){
		$(".outcome").val("");
		$(".screen").html("");
	});
  // minimize (looks kinda cool?)
	$(".min").click(function(){
		$(".cal").stop().animate({
			width: "0px", height: "0px", marginLeft: "700px", marginTop: "1000px"
		}, 500);
		setTimeout(function(){$(".cal").css("display", "none")}, 600);
	});
  //close window. refresh to get back
	$(".close").click(function(){
		$(".cal").css("display", "none");
	})
})

style.css

body{
  background-image: -moz-linear-gradient(top, #137cbc 0%, #30a3d3 25%, #4ba4be 35%, #4094a1 40%, #c2c7aa 50%, #beaa79 100%);
  	background-image: -webkit-linear-gradient(top, #137cbc 0%, #30a3d3 25%, #4ba4be 35%, #4094a1 40%, #c2c7aa 50%, #beaa79 100%);
			background-image: linear-gradient(top, #137cbc 0%, #30a3d3 25%, #4ba4be 35%, #4094a1 40%, #c2c7aa 50%, #beaa79 100%);
	background-attachment: fixed;
	background-repeat: no-repeat;
	color:#c0c0c0;
	font-family: "Helvetica Neue", Arial, sans-serif;
	font-weight: 300;
	font-size:100%;
	letter-spacing: 1.2px;
}
.wrap{
	width:480px;
	margin:50px auto 0;
}
.cal{
	width:480px;
	height:auto;
	padding:10px 0;
	margin: auto;
	background:#232323;
	border:#000 1px solid;
	border-radius:7px;
	-webkit-border-radius:7px;
	-moz-border-radius:7px;
	box-shadow:rgba(0,0,0,0.4) 0px 2px 5px, inset rgba(255,255,255,0.9) 0px 1px 1px -1px;
	-webkit-box-shadow:rgba(0,0,0,0.4) 0px 2px 5px, inset rgba(255,255,255,0.9) 0px 1px 1px -1px;
	-moz-box-shadow:rgba(0,0,0,0.4) 0px 2px 5px, inset rgba(255,255,255,0.9) 0px 1px 1px -1px;
	background-image:-moz-linear-gradient(top, #333333, #1f1f1f);
		background-image:-webkit-linear-gradient(top, #333333, #1f1f1f);
			background-image:linear-gradient(top, #333333, #1f1f1f);
	overflow: hidden;
	text-align: center;
}
.screen{
	width:424px;
	height:93px;
	margin: 12px auto 30px;
	padding:15px 20px;
	color:#c0c0c0;
	text-align: right;
	font-size: 3em;
	letter-spacing: 3px;
	overflow:hidden;
	border:#000 1px solid;
	border-radius:7px;
	-webkit-border-radius:7px;
	-moz-border-radius:7px;
	box-shadow:inset rgba(0,0,0,1) 0px 1px 4px, inset rgba(225,225,225,0.3) 0px -2px 4px -2px;
	-webkit-box-shadow:inset rgba(0,0,0,1) 0px 1px 4px, inset rgba(225,225,225,0.3) 0px -2px 4px -2px;
	-moz-box-shadow:inset rgba(0,0,0,1) 0px 1px 4px, inset rgba(225,225,225,0.3) 0px -2px 4px -2px;
	background-image: -moz-linear-gradient(top, #3e3e3e 0%, #303030 100%);
		background-image: -webkit-linear-gradient(top, #3e3e3e 0%, #303030 100%);
			background-image: linear-gradient(top, #3e3e3e 0%, #303030 100%);
	-moz-box-sizing:border-box;
	-webkit-box-sizing:border-box;
	box-sizing:border-box;
}
.title{
	font-size: 1.2em;
}
.buttons{
	padding:0;
	width:423px;
	margin:auto;
	overflow: hidden;
	list-style: none;
}
.buttons li{
	display:inline;
	float:left;
	padding:0px;
	margin-right:13px;
	margin-bottom:10px;
}
/* remove margin-right on every fourth button */
.buttons li:nth-child(4n){
	margin-right:0;
}
.buttons a{
	display:block;
	width:95px;
	height:68px;
	padding:18px 0 12px;
	color:#c0c0c0;
	font-family: "Myriad Pro", Arial, sans-serif;
	font-size:1.6em;
	font-weight: 500;
	letter-spacing: -2px;
	background-color:#2f2f2f;
	border: #000 1px solid;
	border-radius:5px;
	-webkit-border-radius:5px;
	-moz-border-radius:5px;
	text-align: center;
	text-decoration: none;
	text-shadow:#000 0px -1px 0px;
	box-shadow: inset rgba(255,255,255,0.1) 0px 1px 0px, inset rgba(0,0,0,0.2) 0px -2px 2px;
	-webkit-box-shadow: inset rgba(255,255,255,0.1) 0px 1px 0px, inset rgba(0,0,0,0.2) 0px -2px 2px;
	-moz-box-shadow: inset rgba(255,255,255,0.1) 0px 1px 0px, inset rgba(0,0,0,0.2) 0px -2px 2px;
	background-image:-moz-linear-gradient(top, #363636 0%, #313234 40%, #2f2f2f 100%);
		background-image:-webkit-linear-gradient(top, #363636 0%, #313234 40%, #2f2f2f 100%);
			background-image:linear-gradient(top, #363636 0%, #313234 40%, #2f2f2f 100%);
	-moz-box-sizing:border-box;
	-webkit-box-sizing:border-box;
	box-sizing:border-box;
	cursor: pointer;
}
.buttons a:active{
	box-shadow: inset rgba(0,0,0,0.5) 0px 2px 8px;
	background-image:-moz-linear-gradient(top, #2f2f2f 0%, #363636 100%);
		background-image:-webkit-linear-gradient(top, #2f2f2f 0%, #363636 100%);
			background-image:linear-gradient(top, #2f2f2f 0%, #363636 100%);
}
/* tall = button */
.tall{height:151px !important;}
/* Wide 0 */
.wide{width:205px !important;}
/* shift last row up, because the tall button pushes it down */
.shift{margin-top:-78px;}


/* close, min, max buttons */
.ctrls{
	list-style: none;
	margin:5px 0 0 20px;
	padding:0;
	position: absolute;
}
.ctrls li{
	float:left;
	display:inline;
}
.ctrls li a{
	display: block;
	width:18px;
	height:18px;
	margin-right:10px;
	border-radius:100%;
	box-shadow:rgba(255,255,255,0.3) 0px 0px 1px, inset rgba(0,0,0,1) 0px 1px 2px 1px;
	background-image: -moz-radial-gradient( 9px -4px, #FFF 0px, #fff 2px, rgba(255,255,255,0) 4px), -moz-linear-gradient(bottom, rgba(255,255,255,0.5) 0%, rgba(255,255,255,0) 100%);
	background-image: -webkit-radial-gradient( 9px -4px, #FFF 0px, #fff 2px, rgba(255,255,255,0) 4px), -webkit-linear-gradient(bottom, rgba(255,255,255,0.5) 0%, rgba(255,255,255,0) 100%);
	background-image: radial-gradient( 9px -4px, #FFF 0px, #fff 2px, rgba(255,255,255,0) 4px), linear-gradient(bottom, rgba(255,255,255,0.5) 0%, rgba(255,255,255,0) 100%);
}
.close a{
	background-color:#f32c31;
	
}
.min a{background-color:#f7bf67;}
.max a{background-color:#89cb5a;}
.h1{
	text-align: center;
	color:#fff;
	font-weight: 400;
	font-size: 4em;
	line-height: 0;
	margin-top:80px;
	margin-bottom:-60px;
	text-shadow:#000 0px -1px 0px;
}
p{
	color:#fff;
	text-shadow: #999 0px -1px 0px;
	font-size:1.2em;
	line-height: 2em;
}
a{
	color:#953b3b;
}