how to affect a deffernt element in css

//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; }

#container:hover ~ #cube { background-color: yellow; }

<div id="container">
  <div id="cube">
  </div>
</div>