maptastik/app.js

## app.js
L.mapbox.accessToken = 'pk.eyJ1IjoibWFwdGFzdGlrIiwiYSI6IjNPMkREV1kifQ.2KGPFZD0QaGfvYzXYotTXQ';
var handle = document.getElementById('handle'),
    start = false,
    startTop;

var map = L.mapbox.map('map', 'maptastik.nc2c5lfc',{
      minZoom: 14,
      maxZoom: 20
    })
    .setView([37.976760,-84.526534], 17);

var overlay = L.mapbox.tileLayer('maptastik.fritz-farm', {
      zIndex: 2,
      attribution: '<a href="https://www.lexingtonky.gov/" target="_blank">LFUCG</a>'
    })
    .addTo(map);

document.onmousemove = function(e) {
    if (!start) return;
    // Adjust control.
    handle.style.top = Math.max(-5, Math.min(195, startTop + parseInt(e.clientY, 10) - start)) + 'px';
    // Adjust opacity.
    overlay.setOpacity(1 - (handle.offsetTop / 200));
};

handle.onmousedown = function(e) {
    // Record initial positions.
    start = parseInt(e.clientY, 10);
    startTop = handle.offsetTop - 5;
    return false;
};

document.onmouseup = function(e) {
    start = null;
};

## index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Fritz Farm - Development Plan, 2016</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" />
<link href="https://api.mapbox.com/mapbox.js/v2.4.0/mapbox.css" rel="stylesheet" />
<link href="style.css" rel="stylesheet">
<style>
  body { margin:0; padding:0; }
  #map { position:absolute; top:0; bottom:0; width:100%; }
</style>
</head>
<body>
<div class="title">
  <h1>The Summit at Fritz Farm</h1>
  <h2><a href="https://github.com/ryan-m-cooper/commonwealth-of-openness/files/404070/DP.2016-36.Fritz.Farm.Summit.Lexington.amd.b.pdf">Development Plan 2016-36</a></h2>
</div>
<div id="map"></div>
<div id="control" class="ui-opacity">
  <div id="handle" class="handle"></div>
</div>
<script src="https://api.mapbox.com/mapbox.js/v2.4.0/mapbox.js"></script>
<script src="app.js"></script>
</body>
</html>

## style.css
.title {
  position: absolute;
  right: 20px;
  top: 10px;
  font-family: "Proxima Nova", Montserrat, sans-serif;
  text-align: right;
  max-width: 600px;
  z-index: 10001;
}
h1, h2 {
  font-weight: 100;
  color: #fff;
  line-height: 5px;
  text-shadow: 0 0 0.2em #000;
}
h1 {
  font-size: 2em;
}
h2 {
  font-size: 1em;
}
h2 a {
  color: #f1c40f;
}


.ui-opacity {
  background:#FFF;
  position:absolute;
  left:10px;
  top:70px;
  height:200px;
  width:28px;
  border:1px solid rgba(0,0,0,0.4);
  border-radius:3px;
  z-index:1000;
  }
.ui-opacity .handle {
  position:absolute;
  background:#404040;
  left:0;
  top:20px;
  width:26px;
  height:10px;
  border-radius:1px;
  cursor:pointer;
  cursor:ns-resize;
  }
  .ui-opacity .handle:hover {
    background:#303030;
    }
	L.mapbox.accessToken = 'pk.eyJ1IjoibWFwdGFzdGlrIiwiYSI6IjNPMkREV1kifQ.2KGPFZD0QaGfvYzXYotTXQ';
	var handle = document.getElementById('handle'),
	start = false,
	startTop;

	var map = L.mapbox.map('map', 'maptastik.nc2c5lfc',{
	minZoom: 14,
	maxZoom: 20
	})
	.setView([37.976760,-84.526534], 17);

	var overlay = L.mapbox.tileLayer('maptastik.fritz-farm', {
	zIndex: 2,
	attribution: '<a href="https://www.lexingtonky.gov/" target="_blank">LFUCG</a>'
	})
	.addTo(map);

	document.onmousemove = function(e) {
	if (!start) return;
	// Adjust control.
	handle.style.top = Math.max(-5, Math.min(195, startTop + parseInt(e.clientY, 10) - start)) + 'px';
	// Adjust opacity.
	overlay.setOpacity(1 - (handle.offsetTop / 200));
	};

	handle.onmousedown = function(e) {
	// Record initial positions.
	start = parseInt(e.clientY, 10);
	startTop = handle.offsetTop - 5;
	return false;
	};

	document.onmouseup = function(e) {
	start = null;
	};
	<!DOCTYPE html>
	<html>
	<head>
	<meta charset="utf-8" />
	<title>Fritz Farm - Development Plan, 2016</title>
	<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" />
	<link href="https://api.mapbox.com/mapbox.js/v2.4.0/mapbox.css" rel="stylesheet" />
	<link href="style.css" rel="stylesheet">
	<style>
	body { margin:0; padding:0; }
	#map { position:absolute; top:0; bottom:0; width:100%; }
	</style>
	</head>
	<body>
	<div class="title">
	<h1>The Summit at Fritz Farm</h1>
	<h2><a href="https://github.com/ryan-m-cooper/commonwealth-of-openness/files/404070/DP.2016-36.Fritz.Farm.Summit.Lexington.amd.b.pdf">Development Plan 2016-36</a></h2>
	</div>
	<div id="map"></div>
	<div id="control" class="ui-opacity">
	<div id="handle" class="handle"></div>
	</div>
	<script src="https://api.mapbox.com/mapbox.js/v2.4.0/mapbox.js"></script>
	<script src="app.js"></script>
	</body>
	</html>
	.title {
	position: absolute;
	right: 20px;
	top: 10px;
	font-family: "Proxima Nova", Montserrat, sans-serif;
	text-align: right;
	max-width: 600px;
	z-index: 10001;
	}
	h1, h2 {
	font-weight: 100;
	color: #fff;
	line-height: 5px;
	text-shadow: 0 0 0.2em #000;
	}
	h1 {
	font-size: 2em;
	}
	h2 {
	font-size: 1em;
	}
	h2 a {
	color: #f1c40f;
	}


	.ui-opacity {
	background:#FFF;
	position:absolute;
	left:10px;
	top:70px;
	height:200px;
	width:28px;
	border:1px solid rgba(0,0,0,0.4);
	border-radius:3px;
	z-index:1000;
	}
	.ui-opacity .handle {
	position:absolute;
	background:#404040;
	left:0;
	top:20px;
	width:26px;
	height:10px;
	border-radius:1px;
	cursor:pointer;
	cursor:ns-resize;
	}
	.ui-opacity .handle:hover {
	background:#303030;
	}