What does the ">" (greater-than sign) CSS selector mean?

Solution 1:

> is the child combinator, sometimes mistakenly called the direct descendant combinator.¹

That means the selector div > p.some_class only matches paragraphs of .some_class that are nested directly inside a div, and not any paragraphs that are nested further within. This implies that every element matching div > p.some_class necessarily also matches div p.some_class, with the descendant combinator (space), so the two are understandably often confused.

An illustration comparing the child combinator with the descendant combinator:

div > p.some_class { 
    background: yellow;
}

div p.some_class { 
    color: red;
}

<div>
    <p class="some_class">Some text here</p>     <!-- [1] div > p.some_class, div p.some_class -->
    <blockquote>
        <p class="some_class">More text here</p> <!-- [2] div p.some_class -->
    </blockquote>
</div>

Which elements are matched by which selectors?

Matched by both div > p.some_class and div p.some_class
This p.some_class is located directly inside the div, hence a parent-child relationship is established between both elements. Since "child" is a type of "descendant", any child element is by definition also a descendant. Therefore, both rules are applied.
Matched by only div p.some_class
This p.some_class is contained by a blockquote within the div, rather than the div itself. Although this p.some_class is a descendant of the div, it's not a child; it's a grandchild. Therefore, only the rule with the descendant combinator in its selector is applied.

¹_{Many people go further to call it "direct child" or "immediate child", but that's completely unnecessary (and incredibly annoying to me), because a child element is immediate by definition anyway, so they mean the exact same thing. There's no such thing as an "indirect child".}

Solution 2:

> (greater-than sign) is a CSS Combinator.

A combinator is something that explains the relationship between the selectors.

A CSS selector can contain more than one simple selector. Between the simple selectors, we can include a combinator.

There are four different combinators in CSS3:

descendant selector (space)
child selector (>)
adjacent sibling selector (+)
general sibling selector (~)

Note: < is not valid in CSS selectors.

enter image description here

For example:

<!DOCTYPE html>
<html>
<head>
<style>
div > p {
    background-color: yellow;
}
</style>
</head>
<body>

<div>
  <p>Paragraph 1 in the div.</p>
  <p>Paragraph 2 in the div.</p>
  <span><p>Paragraph 3 in the div.</p></span> <!-- not Child but Descendant -->
</div>

<p>Paragraph 4. Not in a div.</p>
<p>Paragraph 5. Not in a div.</p>

</body>
</html>

Output:

enter image description here

More information about CSS Combinators

Solution 3:

As others mention, it's a child selector. Here's the appropriate link.

http://www.w3.org/TR/CSS2/selector.html#child-selectors

Solution 4:

It matches p elements with class some_class that are directly under a div.

Solution 5:

All p tags with class some_class which are direct children of a div tag.