message: Set min. size of avatar in tutorial messages
diff: @@ -60,6 +60,8 @@ function loadHint (hint: ChallengeHint): HTMLElement {
  elem.style.alignItems = 'center'
  const picture = document.createElement('img')
  + picture.style.minWidth = '64px'
  + picture.style.minHeight = '64px'
  picture.style.width = '64px'
  picture.style.height = '64px'
  picture.style.marginRight = '8px'
  