CSS: adjacent sibling selector (+)

Next-Sibling Combinator (Has Immediate Older Brother X)

aaa + bbb

Match any bbb that immediately comes after aaa. (aaa and bbb are in the same level.)

Each expression can be compound selector.

/* match the b tag that comes immediately after span */
span+b {color:red;}

matches the B:

<div>
<span>A</span>
<b>B</b>
</div>