Only a small subset of CSS properties can be used in a rule with ::grammar-error in its selector:

• color
• background-color
• cursor
• caret-color
• outline and its longhands
• text-decoration and its associated properties
• text-emphasis-color
• text-shadow

In this example, eventual supporting browsers should highlight any flagged grammatical errors with the styles shown.

HTML

<p>My friends is coming to the party tonight.</p>

CSS

::grammar-error {
  text-decoration: underline red;
  color: red;
}

Result

• ::spelling-error