...And What You Don't

The display property can also be used to ‘hide’ elements. At first, it may seem difficult to understand why it would be useful to hide an element, but this is done often in order to create “drop-down menus” or “hidden tips” type content.

To hide an element, set the display properties value to none. Then, to get it to appear, you first write out the selector for the parent container, and add the hover pseudo-selector added. Then, on the same line, use the selector (in this case we are using a .class selector) that references the element(s) you would like to appear. Then, use the display: block; declaration.

CSS
.child-class-to-unhide {
    display: none;
}
.parent-container:hover .child-class-to-unhide {
    display: block;
}