title: How to style annotation lines in Google Charts?
body: <p>I am using <code>Google Charts API</code> to display a vertical line on a <code>LineChart</code> (at a specific point) using <code>annotations</code>. </p>
  
  <p><strong>Is it possible to style the annotation line, to make it more visible</strong> (change its color/thickness, in case I add some vertical <code>gridlines</code> etc.)?</p>
  
  <p><a href="https://i.stack.imgur.com/7lipa.png" rel="nofollow noreferrer">Desired output</a></p>
  
  <p>I'm only interested in the <em>annotation <strong>line</strong> style</em>, not in the <em>annotation text style</em>, as asked in <a href="https://stackoverflow.com/questions/15185308/how-to-change-color-of-annotation-text-in-google-charts">this</a> question.</p>
  
  <p>I have the following code:</p>
  
  <pre><code>function drawVisualization() {
    var data = new google.visualization.DataTable();
    data.addColumn('string', 'x');
    data.addColumn({type: 'string', role: 'annotation'});
    data.addColumn('number', '');
    data.addColumn({
      type: 'boolean',
      role: 'certainty'
      });
  
    data.addRows([
      ["-6", null, 1, true],
      ["-5", null, 2, true],
      ["-4", null, 4, true],
      ["-3", null, 8, true],
      ["-2", null, 7, true],
      ["-1", null, 7, true],
      ["0", '', 8, true],
      ["1", null, 4, false],
      ["2", null, 2, false],
      ["3", null, 3, false],
      ["4", null, 3, false],
      ["5", null, 1, false],
      ["6", null, 1, false]
    ]);
  
    new google.visualization.LineChart(document.getElementById('visualization')).
  draw(data, {
        curveType: 'function',
        width: 500,
        height: 400,
        annotations: {
          style: 'line'
        }
    });
  }
  </code></pre>
  
  <p>You can play with the code in this <a href="http://jsfiddle.net/NC37X/284/" rel="nofollow noreferrer">fiddle</a>.</p>