Answers for "overlay div on another div hover"

css div overlay div

#container { //goes to the bottom
  width: 100px;
  height: 100px;
  position: relative;
}
#div1{ //comes to the top
  width: 100%;
  height: 100%;
  position: absolute;
  top: 0;
  left: 0;
  z-index: 10;
}

hover on one div affect another

//cube is directly inside the container:
#container:hover > #cube { background-color: yellow; }

//cube is next to (after containers closing tag) the container:
#container:hover + #cube { background-color: yellow; }

//If the cube is somewhere inside the container:
#container:hover #cube { background-color: yellow; }

//If the cube is a sibling of the container:
#container:hover ~ #cube { background-color: yellow; }