Add Opacity (#1603)

Author: jamesnw

features/opacity.yml

@@ -0,0 +1,9 @@
+name: opacity
+description: The `opacity` CSS property sets the transparency of an element.
+spec: https://drafts.csswg.org/css-color-3/#transparency
+group: css
+status:
+  compute_from: css.properties.opacity
+compat_features:
+  - css.properties.opacity
+  - css.properties.opacity.percentages

features/opacity.yml.dist

@@ -0,0 +1,42 @@
+# Generated from: opacity.yml
+# Do not edit this file by hand. Edit the source file instead!
+
+status:
+  baseline: high
+  baseline_low_date: 2015-07-29
+  baseline_high_date: 2018-01-29
+  support:
+    chrome: "1"
+    chrome_android: "18"
+    edge: "12"
+    firefox: "1"
+    firefox_android: "4"
+    safari: "2"
+    safari_ios: "1"
+compat_features:
+  # ⬇️ Same status as overall feature ⬇️
+  # baseline: high
+  # baseline_low_date: 2015-07-29
+  # baseline_high_date: 2018-01-29
+  # support:
+  #   chrome: "1"
+  #   chrome_android: "18"
+  #   edge: "12"
+  #   firefox: "1"
+  #   firefox_android: "4"
+  #   safari: "2"
+  #   safari_ios: "1"
+  - css.properties.opacity
+
+  # baseline: high
+  # baseline_low_date: 2020-07-28
+  # baseline_high_date: 2023-01-28
+  # support:
+  #   chrome: "78"
+  #   chrome_android: "78"
+  #   edge: "79"
+  #   firefox: "70"
+  #   firefox_android: "79"
+  #   safari: "13.1"
+  #   safari_ios: "13.4"
+  - css.properties.opacity.percentages