Check for CSS variable support (#28256)
Check for CSS variable support (#28256)

* Check for CSS variable support

* Update extensions/amp-story/1.0/amp-story.js

Co-authored-by: Gabriel Majoulet <61bf5be2966d6eaf52eb20c76d89ea6390af5366@gmail.com>

Co-authored-by: Gabriel Majoulet <61bf5be2966d6eaf52eb20c76d89ea6390af5366@gmail.com>
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