Setting default res for HTML

Ok in the GameX.html.template in the same folder, there are

.wrapper{
	position: relative;
	margin: 1em auto 10px auto;
	text-align: center;
	min-width: 640px;
	min-height: 480px; 
	max-width: 95%;
	display: block; 
	align-items: center;
	position: relative;
	text-align: center;
	justify-content: center;
}

and

#canvas:not([fullscreen]) {
  padding-right: 0;
  margin-left: auto;
  margin-right: auto;
  width: 100%;
}

Changing these values works great.
Thanks for showing me the way, svv3dUDN !