CSS nth-child for greater than and less than

:nth-child() doesn’t work on classes, it looks for the element itself. You’d need to wrap the .container divs by a wrapper and use the following:

.wrapper div:nth-child(n+3) {
   /* put your styles here... */
}

<div class="wrapper">
    <div class="container"></div>
    <div class="container"></div>
    <div class="container"></div>
    <div class="container"></div>
</div>

Working Demo.

Clarifying on :nth-child()

Using .container:nth-child(n+3) may or may not work. Because, :nth-child() pseudo-class represents nth child element matching the selector (.container in this case).

If the .container element isn’t the nth-child of its parent, it won’t be selected.

From the Spec:

The :nth-child(an+b) pseudo-class notation represents an element
that has an+b-1 siblings before it in the document tree, for any
positive integer or zero value of n, and has a parent element.

Consider this example:

<div class="parent">
    <div>1st</div>
    <div>2nd</div>
    <div>3rd</div>
    <div class="container">4th</div>
    <div class="container">5th</div>
    <div class="container">6th</div>
    <div>7th</div>
    <div class="container">8th</div>
    <div>9th</div>
</div>

In this case, .container:nth-child(2) won’t select the 2nd div.container element (which has 5th content). Because that element is not the 2nd child of its parent, in parent’s children tree.

Also, .container:nth-child(n+3) will select all the div.container elements because n starts from 0 for the first element in the parent’s children tree, and the first div.container is the 4th child of its parent.

n starts from 0

n = 0: (0 + 3) = 3 => 3rd element
n = 1: (1 + 3) = 4 => 4th element
n = 2: (2 + 3) = 5 => 5th element
...

Hence div.container:nth-child(n+3) represents all the 3rd, 4th, 5th, … child elements matching div.container selector.

Online Demo.