Revert "Define background colors with transparency"

This reverts commit b6a4acd57d244105a7f9bfcdd6a5fc0c8827faf6.

Reason for revert: https://imgur.com/nTIFuiL

Change-Id: I308da684c1105122aa99d8481a41ac426d584c79

polygerrit-ui/app/styles/themes/app-theme.html

diff --git a/polygerrit-ui/app/styles/themes/app-theme.html b/polygerrit-ui/app/styles/themes/app-theme.html
index c7f1346..53827b5 100644
--- a/polygerrit-ui/app/styles/themes/app-theme.html
+++ b/polygerrit-ui/app/styles/themes/app-theme.html
@@ -43,8 +43,8 @@
   /* background colors */
   /* primary background colors */
   --background-color-primary: #ffffff;
-  --background-color-secondary: rgba(0, 0, 0, 0.025);
-  --background-color-tertiary: rgba(0, 0, 0, 0.05);
+  --background-color-secondary: #f8f9fa;
+  --background-color-tertiary: #f1f3f4;
   /* directly derived from primary background colors */
   --chip-background-color: var(--background-color-tertiary);
   --default-button-background-color: var(--background-color-primary);

polygerrit-ui/app/styles/themes/dark-theme.html

diff --git a/polygerrit-ui/app/styles/themes/dark-theme.html b/polygerrit-ui/app/styles/themes/dark-theme.html
index 61b2dc6..80243dc 100644
--- a/polygerrit-ui/app/styles/themes/dark-theme.html
+++ b/polygerrit-ui/app/styles/themes/dark-theme.html
@@ -43,8 +43,8 @@
       /* background colors */
       /* primary background colors */
       --background-color-primary: #202124;
-      --background-color-secondary: rgba(255, 255, 255, 0.05);
-      --background-color-tertiary: rgba(255, 255, 255, 0.1);
+      --background-color-secondary: #2f3034;
+      --background-color-tertiary: #3b3d3f;
       /* directly derived from primary background colors */
       /*   empty, because inheriting from app-theme is just fine
       /* unique background colors */