Adjust dark-theme coverage colors to contrast less

The existing colors in the dark theme are just the same values as in the
light theme. To generate these colors, I took the highly unscientific
method of:

- load the color value in a color picker
- convert to HSL
- invert the lightness (so 82% -> 18%)
- bump the values slightly because our background isn't pure black

The covered color was 82% lightness and is now 21%, the not-covered
color was 91% lightness and is now 11%.

Change-Id: I13d861514ea5674fe34012227519acacf02eca4c
diff --git a/polygerrit-ui/app/styles/themes/dark-theme.html b/polygerrit-ui/app/styles/themes/dark-theme.html
index cfc1f62..80243dc 100644
--- a/polygerrit-ui/app/styles/themes/dark-theme.html
+++ b/polygerrit-ui/app/styles/themes/dark-theme.html
@@ -98,8 +98,8 @@
       --light-rebased-add-highlight-color: #487165;
       --light-remove-add-highlight-color: #2f3f2f;
       --light-remove-highlight-color: #320404;
-      --coverage-covered: #e0f2f1;
-      --coverage-not-covered: #ffd1a4;
+      --coverage-covered: #112826;
+      --coverage-not-covered: #6b3600;
 
       /* syntax colors */
       --syntax-attr-color: #80cbbf;