CSS

max width css

#parent {
  background: lightblue;
  width: 300px;
}

#child {
  background: gold;
  width: 100%;
  max-width: 1400px;
}

max-width

width: min(100%, 70rem);

CSS Height, Width and Max-width

div {
  height: 200px;
  width: 50%;
  background-color: powderblue;
}