title: Vega custom style for text mark
body: <p>So as usual I have trouble applying what I read in the Vega documentation. It seems like several parts are missing or I don't know how to read it.</p>
  
  <p>Problem: I have a text mark corresponding to a point in a scatter plot. Imagine one red dot with "Ferrari" written next to it. I want to style the text to be bigger and of a different color.</p>
  
  <p>If I go to the Vega documentation, to the marks section, I see a promising property there: <code>style</code> and I read: <strong>Style</strong> -- A string or array of strings indicating the name of custom styles to apply to the mark. A style is a named collection of mark property defaults defined within the configuration. That sounds perfect.</p>
  
  <p>I then went on to create the following in the config object:</p>
  
  <pre><code>config': {
        'axis': {
          'labelColor': '#b5bcc8',
          'labelFontSize': 15,
          'labelFont': '(quatro)',
          'titleColor': '#b5bcc8',
          'titleFontSize': 15,
          'titleFont': '(quatro)',
          'titlePadding': 20,
          'tickColor': '#b5bcc8',
          'domainColor': '#b5bcc8'
        },
        'custom': {
          'textFontSize': 22
        }
  }
  </code></pre>
  
  <p>Then apply this custom style to the text mark, as suggested:</p>
  
  <pre><code>{
     'name': 'product_label',
     'type': 'text',
     'from': { 'data': 'salesData' },
     'style': 'custom',
     'encode': {
        'enter': {
           'x': { 'scale': 'x', 'field': 'month', 'offset': 8 },
           'y': { 'scale': 'y', 'field': 'salesTotal', 'offset': -5 },
              'text': { 'field': 'name' },
              'fill': { 'value': 'black' }
          }
        }
    }
  </code></pre>
  
  <p>Of course, I made a lot of assumptions here, as I have no examples for this. I assumed <em>named collection</em> means an object. I assumed <em>textFontSize</em> is a valid object property for Vega. But these assumptions may as well be wrong. </p>