title: Add class/style to active button in VueJS
body: <p><em>This isn't tied to the router menu.</em></p>
  <p>I have a Price sheet witch consists of 3 sub-sheets.</p>
  <p>Above the single visible sheet is are 3 buttons which, when clicked, show the corresponding sheet.</p>
  <p><a href="https://i.imgur.com/slitOou.png" rel="nofollow noreferrer">The design of the pricesheet</a></p>
  <p>I was lookin at the Vue style bindings but they only trigger on <code>True / False</code> and not on the value of the single variable.</p>
  <p>Of course there's the option to have a data() variable for each button and upon change set the other two to false, but maybe there's a way to bring that repeated code to a single variable?</p>