Adjacent sibling combinator A + B

The Adjacent sibling combinator represents a "B" element that is placed immediately after a "A" element.

Syntax

A + B{ preperties }

The adjacent sibling combinator is made of the "plus sign" (+) character that separates two sequences of simple selectors.
The elements represented by the two sequences share the same parent in the document tree.

[style.css]

 h1 + p{
   background-color: yellow;
 }

[index.html]

<body>
<h1>Header</h1>
<p>This is a paragraph.</p>
<p>This is a paragraph.</p>
</body>

The CSS Selectors Level 3 specification defines the Adjacent sibling combinator in 8.3.1. Adjacent sibling combinator.