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The CSS cascade selects a winning declaration for each property on each element from the declarations that apply. Its ordering includes origin and importance, CSS cascade layers, CSS specificity and source order. Later comparisons settle ties left by earlier priorities; a rule's position at the end of a file is therefore only one part of the decision.^[ref]

Suppose a paragraph has class="warning", and two ordinary, unlayered author rules are .warning { color: red; } followed by p { color: blue; }. Both match, but the class selector has greater CSS specificity, so red wins despite the blue rule's later position. If the second rule is p { color: blue !important; }, its importance instead makes blue win over the normal red declaration. These examples hold other styling inputs fixed.

Origins represent different participants, including the browser's default rules, the user and the page author. For example, important user declarations outrank important author declarations, allowing user styling to take priority in that part of the system. Layer order is also a separate input; adding selectors with larger specificity is not a substitute for understanding that earlier comparison.^[ref]

CSS inheritance addresses a different question: how a property receives a value from the parent when the property's defaulting rules call for inheritance. A parent being red does not create a competing selector match on every descendant. Keeping applicability, cascade selection and inheritance distinct explains why an element can inherit a color even though no rule explicitly selects that element.

CSS inheritance propagates property values from a parent element to a child when the property's defaulting rules call for it. For an inherited property, the child normally receives the parent's CSS computed value if it has no applicable declaration supplying another value. A property that is not inherited instead normally uses its CSS initial value. The root has no parent from which to inherit.^[ref]

Suppose a parent has font-size: 20px and a child specifies font-size: 150%. The child computes to 30 CSS pixels. If a grandchild merely inherits font size, it receives 30 pixels; it does not multiply the original 150 percent again. This is why inheriting a computed value differs from copying the parent's source text.

The keyword inherit can request inheritance even for a property that does not normally inherit. Thus a width declaration with that keyword is a deliberate instruction, whereas omitting width does not automatically copy the parent's width. The exact result still depends on that property's value-processing rules.^[ref]

Importance does not spread down the tree as selector priority. If a parent obtains red from an important color declaration, a child with its own ordinary blue color declaration can be blue. The parent contributed a possible inherited value; it did not create an important declaration on the child. Distinguishing CSS inheritance from the CSS cascade explains both shared styling and local overrides.

A CSS initial value is the value defined as a property's starting point by its specification. It participates in defaulting when an element has no other specified value under the applicable rules. It is distinct from a browser's default stylesheet declaration and from the value obtained by CSS inheritance.^[ref]

For example, the initial value of display is inline, while a browser normally supplies styling that makes a paragraph block-level. Setting p { display: initial; } requests the property's initial value, rather than restoring the browser's usual paragraph appearance. The paragraph's HTML element semantics remain separate from that display choice.

The keyword initial explicitly requests this starting value. inherit requests the parent's computed value instead, and unset chooses inheritance for inherited properties and the initial value for non-inherited properties. Thus these keywords can produce different results even when they appear in the same selector and win the same CSS cascade comparison.^[ref]

Initial values also need their normal processing. A width initially set to auto still requires the appropriate sizing algorithm; initial does not mean that every property begins as zero or already has a final pixel size. The sequence from defaulting through computation to the CSS used value explains how a specification-defined starting value becomes a concrete rendering.

A CSS property value is a value considered or assigned for a CSS property. Its representation changes through value processing: declarations supply candidates, the CSS cascade chooses among applicable candidates, defaulting supplies missing values, and computation and layout resolve further details. The CSS computed value and CSS used value consequently describe different stages.^[ref]

Take width: 50%. In a simple block layout, its computed representation can retain a percentage, while the used width depends on the containing width. A 400-CSS pixel containing block gives 200 pixels; changing that block to 600 pixels gives 300. Copying the source string alone would miss why the physical layout changed.

Inheritance can resolve another value before that stage. If a parent's computed font size is 20px and its child specifies font-size: 150%, the child can compute to 30px. That child's descendant inheriting the font size receives the computed result, rather than repeatedly multiplying by the original percentage merely because it is further down the tree.^[ref]

Validity is property-specific. A syntactically readable width: blue is not a valid width value, and its failure does not establish a used width of blue or zero. Initial values, CSS inheritance and other applicable declarations determine the result under the relevant rules. Stating the value stage prevents a source token, a computed representation and a measured rendering from being conflated.