Answers for "css how to overlay"

overlay css

#overlay {
  position: fixed; /* Sit on top of the page content */
  display: none; /* Hidden by default */
  width: 100%; /* Full width (cover the whole page) */
  height: 100%; /* Full height (cover the whole page) */
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: rgba(0,0,0,0.5); /* Black background with opacity */
  z-index: 2; /* Specify a stack order in case you're using a different order for other elements */
  cursor: pointer; /* Add a pointer on hover */
}

overlay a box in css

html, body{
  min-height: 100%;
}
body{
  position: relative;
}
.overlay{
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 10;
  background-color: rgba(0,0,0,0.5); /*dim the background*/
}