indeterminate(:indeterminate)
The :indeterminate CSS pseudo-class represents any <input type=”checkbox”> element whose indeterminate DOM property is set to true by JavaScript. In addition, in some browsers, it can be used to match to <progress> elements in an indeterminate state.
Example
<!DOCTYPE html> <html> <head> <style> input, span { background: red }:indeterminate,:indeterminate + span { background: limegreen } </style> </head> <body> <p> <input type=checkbox><span> Everything in this paragraph should have a green background. </span> </p> <script> document.getElementsByTagName("input")[0].indeterminate = true; </script> </body> </html>