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

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

  --wContent: 100vw;
  --hContent: 100vh;
  margin: 0;
  padding: 0;
  height: 100vh;
}
  
#ow
{ 
  padding: 0;
  display: inline-block;
}

#cw
{
  display : inline-block;
}

#cw canvas
{
  max-width: 100vw;
  max-height: 100vh;
}