body
{ display: flex;
  min-height: 98vh;
  flex-direction: column;
}

button { font-size: 1.5em; }

#footer
{ text-align: center;
  margin: 0.8em;
  color: firebrick;
}

ul, ol, p
{ max-width: 68em;
  margin-left: auto;
  margin-right: auto;
}

p { margin-top: 0.5em; margin-bottom: 0.5em; }
h1 { text-align: center; }

canvas
{ width: 100vw;
  height: 100vh;
  display: block;
}

@media (min-width: 50em)
{
  #topmenu li
  { display: inline-block;
    background-color: #DDDDDDFF;
    padding: 0.2em;
    border: solid yellow;
  }

  #topmenu { text-align: center; max-width: 100em; }
  #bottommenu { display: none; }
}

@media (max-width: 50em)
{
  #topmenu { display: none; }

  #bottommenu li
  { display: inline-block;
    background-color: #DDDDDDFF;
    padding: 0.2em;
    border: 0.2em solid Green;
  }
}