title: How to make Stroke opacity work in OpenLayers 3
body: <p>I cannot get Stroke opacity working in OpenLayers 3 no matter what I try. What I try to achieve is to draw a line to OSM tile map with 0.5 opacity.</p>
  
  <p>Here is sample code:</p>
  
  <pre><code>var lineString = new ol.geom.LineString([
     [4.9020, 52.3667],
     [4.9030, 52.3667],
     [4.9040, 52.3667],
     [4.9050, 52.3667]
  ]);
  lineString.transform('EPSG:4326', 'EPSG:3857');
  
  var lineLayer = new ol.layer.Vector({
      source: new ol.source.Vector({
          features: [new ol.Feature({
              geometry: lineString,
              name: 'Line'
          })]
      }),
      style: new ol.style.Style({
          stroke: new ol.style.Stroke({
              color: 'yellow',
              opacity: 0.5,
              width: 15
          })
      })
  });    
  
  var view = new ol.View({
      center: ol.proj.transform([4.9020, 52.3667], 'EPSG:4326','EPSG:3857'),
     zoom: 18
  });
  
  var map = new ol.Map({
    layers: [
      new ol.layer.Tile({
        source: new ol.source.OSM()
      }),
      lineLayer
    ],
    target: 'map',
    controls: ol.control.defaults({
      attributionOptions: /** @type {olx.control.AttributionOptions} */ ({
        collapsible: false
      })
    }),
    view: view
  });
  </code></pre>
  
  <p>You can see it here:
  <a href="http://jsfiddle.net/abgcvqw3/1/" rel="nofollow">http://jsfiddle.net/abgcvqw3/1/</a></p>