Anastasia's questions

var notes = ['do', 'do#', 're', 're#', 'mi', 'fa', 'fa#',
  'sol', 'sol#', 'la', 'la#', 'si'
];

function stepUp() {
  var text = document.getElementById('textarea');
  if (typeof text.count == 'undefined') {
    text.count = 0;
  } else {
    text.count++;
  }

  if (text.count == notes.length) {
    text.count = 0;
  }
  text.innerHTML = notes[text.count];
}

function stepDown() {
  var text = document.getElementById('textarea');
  text.count--;

  if (text.count == notes.length) {
    text.count = 0;
  }

  if (text.count < 0) {
    text.count = 11;
  }
  text.innerHTML = notes[text.count];
}

/* Load file*/
function load_song() {
  var fileToLoad = document.getElementById("load_button").files[0];
  var fileReader = new FileReader();
  fileReader.onload = function(fileLoadedEvent) {
    var textFromFileLoaded = fileLoadedEvent.target.result;
    document.getElementById("textarea").value = textFromFileLoaded;
  };
  fileReader.readAsText(fileToLoad, "UTF-8");
}

body {
  font-family: Arial, sans-serif;
  background-color: #333;
  color: #ddd;
  text-align: center;
}

container {
  display: flex;
  margin: 2vmin;
  position: relative;
  top: 3vmin;
}

<div class="container">
  <textarea id="textarea" rows="5" cols="50">---</textarea>
</div>

<button onclick="stepUp()" class="stepUp_Button">Up</button>
<button onclick="stepDown()" class="stepDown_Button">Down</button>

<!-- Load button -->
<span>Load File:&nbsp;</span>
<input type="file" id="load_button">
<button class="load_button" onclick="load_song()">Load</button>