Combining :not() selectors in CSS

Selectors level 3 does not allow anything more than a single simple selector within a :not() pseudo-class. As a jQuery selector, it works because jQuery extends its :not() functionality to allow any selector (like the .not() method).

However, your second syntax is one of the proposed enhancements to :not() in Selectors 4, and works equivalently to your first. Although the example (shown as of this writing anyway) shows a chain of :not() selectors, the proposal says:

The negation pseudo-class, :not(X), is a functional notation taking a selector list as an argument. It represents an element that is not represented by its argument.

Here a selector list is simply a comma-separated list of selectors.

If you need to negate selectors that contain combinators (>, +, ~, space, etc, for example div p), you can't use :not() in CSS; you'll have to go with the jQuery solution.

Although the marked answer is true I just want to point out that you can achieve what you want using css also but just in a different way. Instead of using not you can select those and unapply the stuff you don't want.

#table tr {
    /* general case styling */
    color: blue;
}
#table tr:nth-child(3),
#table tr:nth-child(4) {
    color: black;
}