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; }