body {
  background-color: #555;
  font-family: sans-serif;
  overflow: hidden;

  display: flex;
  justify-content: center;
  align-items: center;

  --bodymargin : 10px;
  --wContent: calc(100vw - 2*var(--bodymargin));
  --hContent: calc(100vh - 2*var(--bodymargin));
  margin: 0;
  padding: 0;
  height: 100vh;
}

#ow
{ padding: var(--bodymargin);
  display: inline-block;
}

#cw
{
  display : inline-block;
}

#cw canvas
{
  max-width: var(--wContent);
  max-height: var(--hContent);
  box-shadow: 1px 1px 2px 2px rgba(33, 33, 33, .2);

}