Answers for "how to change the display of element when hover on another"

how to change another element on hover

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

// If 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; }

on hover display another div css

.showme {
  display: none;
}

.showhim:hover .showme {
  display: block;
}


<div class="showhim">HOVER ME
  <div class="showme">hai</div>
</div>