/**
   * Initiate 3 variables (seconds, tens, interval)
   * Give a starting value of 0 for seconds and tens
   * Use the appropriate variable type for each
   */

  /**
   * Get the DOM elements for the stopwatch and save them in variables
   * Use the appropriate variable type for each
   *
   * Hint: There are 3 buttons and 2 numbers to manipulate
   */

  /**
   * Create a function, which is waiting for the user to press the 'Start' button.
   * When pressed, set the timer run `runStopwatch` function every 10ms.
   */
  buttonStart.onclick = () => {}

  /**
   * Create a function, which is waiting for the user to press the 'Stop' button.
   * When pressed, clear the interval.
   */
  buttonStop.onclick = () => {}

  /**
   * Create a function, which is waiting for the user to press the 'Reset' button.
   * When pressed, clear the interval, reset the seconds and tens to 0.
   *
   * Hint: Don't forget to concatenate a leading '0'.
   */
  buttonReset.onclick = () => {}

  /**
   * Build the `runStopwatch` function.
   */
  const runStopwatch = () => {
    // Increment the tens.
    /**
     * Display updated tens and seconds.
     * Make sure, that the tens and seconds are always two digits long.
     *
     * Hint: there are 4 cases you need to handle every time the function runs.
     */
  }