CSS: “right”: “X” is not a “right” value.

An invalid value was assigned to the CSS right property, meaning the validator does not recognize the value you provided.

The CSS right property specifies the horizontal offset of a positioned element from the right edge of its containing block. It only accepts specific value types: a length (e.g., 10px, 2em), a percentage (e.g., 50%), auto, inherit, initial, unset, or revert. Any other value — such as a typo, a missing unit, or an unsupported keyword — will trigger this validation error.

A common mistake is forgetting the unit after a number. In CSS, 0 is the only length value that can be written without a unit. Writing something like right: 10 instead of right: 10px is invalid. Another common cause is using an unrecognized keyword or passing a value meant for a different property.

Invalid Example

<div style="position: absolute; right: 10;">
  This box has an invalid right value.
</div>

The value 10 is missing a unit, so the validator rejects it.

Fixed Example

<div style="position: absolute; right: 10px;">
  This box is correctly positioned.
</div>

Adding a valid unit like px, em, rem, or % resolves the issue. If you intended no offset, use right: 0 or right: auto.

Learn more:

MDN Reference

CSS right property - MDN

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MDN Reference

CSS Values and Units - MDN

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