<!DOCTYPE html>
<html lang='en'>
<head>
  <meta charset='UTF-8'>
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Flat Calculator</title>
  <link href='css/calculator.css' rel='stylesheet' />
</head>
<body>
  <div id='calculator_app'></div>
  <script id='calculator_template' type='text/ractive'>
    <input class='result' on-enter='calculate()' type='text' value='{{result}}' />
    <table class='buttons'>
      <tbody>
        {{#each buttons:y}}
        <tr>
          {{#each buttons[y]:x}}
          <td class='button' on-tap='tap(x, y)'>{{buttons[y][x]}}</td>
          {{/each}}
        </tr>
        {{/each}}
      </tbody>
    </table>
  </script>
  <script src='js/ractive.min.js'></script>
  <script src='js/ractive-events-keys.js'></script>
  <script src='js/ractive-events-tap.umd.js'></script>
  <script src='js/calculator.js'></script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Flat Calculator</title>
  <link href="css/calculator.css" rel="stylesheet" />
</head>
<body>
  <div id="calculator_app"></div>
  <script id="calculator_template" type="text/ractive">
    <input class="result" on-enter="calculate()" type="text" value="{{result}}" />
    <table class="buttons">
      <tbody>
        {{#each buttons:y}}
        <tr>
          {{#each buttons[y]:x}}
          <td class="button" on-tap="tap(x, y)">{{buttons[y][x]}}</td>
          {{/each}}
        </tr>
        {{/each}}
      </tbody>
    </table>
  </script>
  <script src="js/ractive.min.js"></script>
  <script src="js/ractive-events-keys.js"></script>
  <script src="js/ractive-events-tap.umd.js"></script>
  <script src="js/calculator.js"></script>
</body>
</html>

Use double quote in html
Use double quote in html
