:not() :is() and :where()

:not(selector) selects elements that do not match the given selector. It inverts the selection.

Modern CSS allows multiple arguments inside :not() — it matches elements that match none of the listed selectors:

The specificity of :not() is the specificity of its most specific argument. :not(.active) has class-level specificity (0,1,0).

:is() matches any element that matches any of a list of selectors. It simplifies grouping and reduces repetition.

:is() takes the specificity of its most specific argument. If the list contains an ID selector, the whole rule has ID specificity.

:is() uses forgiving selector parsing: if any selector in the list is invalid, it is silently ignored and the rest still apply. Regular comma-separated selectors fail entirely if one is invalid.

:where() works exactly like :is() but has zero specificity. It is designed for utility classes and reset styles that should be easy to override.

:where() is ideal for CSS resets and base styles that should never win specificity battles:

Summary of specificity behavior:

• :is() — highest specificity among arguments
• :where() — always zero specificity
• :not() — highest specificity among arguments

Combine them for precise, readable selectors:

:is() and :where() are supported in all modern browsers. :not() with multiple arguments is supported in modern browsers. Avoid in projects requiring IE11 support.

:not() inverts selection and accepts multiple arguments. :is() matches any of a list with the highest specificity in that list. :where() does the same but with zero specificity — perfect for resets. All three use forgiving parsing, silently ignoring invalid selectors.