Target Selector

Applies styling when the selector is in a target state. Which is to say it is the target of a hash mark in the URL.

#container:target {
  background-color: #f6f6f6;
}

Adjacent Sibling Selector

From CSS2:

h2 + p {}
Will select the second element when it immediately follows the first. (Reference)

General Sibling Selector

From CSS3:

h2 ~ p {}
Selects all p’s that share a parent with the h2. (Reference)