https://github.com/GarethPW/YouTube-Player-Frosted-Glass

Safari currently supports this style by default.

In order to make this style work in Chrome or Opera, you must enable the flag, #enable-experimental-web-platform-features:

• Chrome: chrome://flags/#enable-experimental-web-platform-features
  
• Opera: opera://flags/#enable-experimental-web-platform-features
  

If you have any suggestions, bugs to report, or other comments, please remember to leave feedback below!

v1.0.0:
-Initial release.

v1.1.0:
-Added effect to subtitles.

v1.2.0:
-Added blur radius style setting.

v1.2.1:
-Highlight annotations no longer blur backdrop.
-Tweaks to captions.

v1.3.0:
-Added effect to channel cards.

v1.3.1:
-Fixes for transitions.
-CSS cleaned up.

v1.3.2:
-Removed unnecessary backdrop blur from ytp-preview.
-RegExp improvement.

v1.4.0:
-Card teasers now blur backdrop.

v1.5.0:
-iv-promo annotations now blur backdrop.

v1.6.0:
-Speech annotations now blur backdrop.
-Fix for annotation text opacity.

v1.6.1:
-Reverted speech annotation change.

v1.7.0:
-All expandable cards now exhibit frosted glass effect.

v1.8.0:
-Effect added to volume slider.
-Effect added to scrubbing/next video preview.

v1.8.1:
-Enlarged progress bar and hover progress fix.

v1.8.2:
-Reverted progress bar fix due to now being seemingly unnecessary.

v1.8.3:
-Fix for hover progress being incorrectly visible.

v1.9.0:
-Added effect to fresca sidebar.

v1.10.0:
-Added effect to cards playlist counts.

v1.11.0:
-Added effect to video wall list labels.

v1.12.0:
-Small improvement to transitions and performance.

v1.12.1:
-Fixed issue where annotations on Chrome and Opera would blur a region slightly taller than their backdrop. (Chrome bug)
-Fixed issue where annotation text would have no transparency; increased opacity from intended 0.8 to 0.9
-Background opacity of captions is now dictated by YouTube's player settings instead of the user style
-Minor code clean-up

v1.12.2:
-Fixed issue where cards on Chrome and Opera would blur a region slightly larger than their backdrop. (Chrome bug)

v1.13.0:
-Opacity of cards drawer increased to 0.9
-Added frosted glass effect to offline slate and playlist menu

v1.14.0:
-Added frosted glass to pause overlay
-Small tweak to RegEx

v1.15.0:
-Added effect to subscription promo
-Small tweak to RegEx