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;
};