input: Write a python function to create a 3x3 matrix of digits from 1 to 9 in HTML format.
  assert create_html_matrix() == '''<html>
      <head>
          <title>Digit 3x3 Matrix</title>
          <style>
              table{
                  border:1px solid black; 
                  width: 50px; 
                  height:50px;
              }
          </style>
      </head>
      <body>
          <h1>Digit 3x3 Matrix</h1>
          <table>
              <tr>
                  <td>1</td><td>2</td><td>3</td>
              </tr>
              <tr>
                  <td>4</td><td>5</td><td>6</td>
              </tr>
              <tr>
                  <td>7</td><td>8</td><td>9</td>
              </tr>
          </table>
      </body>
  </html>'''
  assert create_html_matrix() != ''
output: def create_html_matrix():
      return '''<html>
      <head>
          <title>Digit 3x3 Matrix</title>
          <style>
              table{
                  border:1px solid black; 
                  width: 50px; 
                  height:50px;
              }
          </style>
      </head>
      <body>
          <h1>Digit 3x3 Matrix</h1>
          <table>
              <tr>
                  <td>1</td><td>2</td><td>3</td>
              </tr>
              <tr>
                  <td>4</td><td>5</td><td>6</td>
              </tr>
              <tr>
                  <td>7</td><td>8</td><td>9</td>
              </tr>
          </table>
      </body>
  </html>'''