hover on one div affect another

1//cube is directly inside the container:
2#container:hover > #cube { background-color: yellow; }
3
4//cube is next to (after containers closing tag) the container:
5#container:hover + #cube { background-color: yellow; }
6
7//If the cube is somewhere inside the container:
8#container:hover #cube { background-color: yellow; }
9
10//If the cube is a sibling of the container:
11#container:hover ~ #cube { background-color: yellow; }

1#container:hover ~ #cube { background-color: yellow; }
2

1#a:hover + #b {
2    background: #ccc
3}
4
5<div id="a">Div A</div>
6<div id="b">Div B</div>

1.showme {
2  display: none;
3}
4
5.showhim:hover .showme {
6  display: block;
7}
8
9
10<div class="showhim">HOVER ME
11  <div class="showme">hai</div>
12</div>