Move coverage colors to theme css vars

Change-Id: I80dde321bb923ddca32773350b8c8464043f96cd
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
index 31c467f..1446fd4 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
@@ -294,13 +294,16 @@
         display: none;
       }
       .lineNum.COVERED {
-         background-color: #E0F2F1;
+         background-color: var(--coverage-covered, #e0f2f1);
       }
       .lineNum.NOT_COVERED {
-        background-color: #FFD1A4;
+        background-color: var(--coverage-not-covered, #ffd1a4);
       }
       .lineNum.PARTIALLY_COVERED {
-        background: linear-gradient(to right bottom, #FFD1A4 0%, #FFD1A4 50%, #E0F2F1 50%, #E0F2F1 100%);
+        background: linear-gradient(to right bottom, var(--coverage-not-covered, #ffd1a4) 0%,
+                                                     var(--coverage-not-covered, #ffd1a4) 50%,
+                                                     var(--coverage-covered, #e0f2f1) 50%,
+                                                     var(--coverage-covered, #e0f2f1) 100%);
       }
 
       /** BEGIN: Select and copy for Polymer 2 */
diff --git a/polygerrit-ui/app/styles/themes/app-theme.html b/polygerrit-ui/app/styles/themes/app-theme.html
index d3ae6b0..66a11a7 100644
--- a/polygerrit-ui/app/styles/themes/app-theme.html
+++ b/polygerrit-ui/app/styles/themes/app-theme.html
@@ -134,6 +134,8 @@
   --light-rebased-add-highlight-color: #eef;
   --light-remove-add-highlight-color: #fff8dc;
   --light-remove-highlight-color: #ffebee;
+  --coverage-covered: #e0f2f1;
+  --coverage-not-covered: #ffd1a4;
 
   /* syntax colors */
   --syntax-attr-color: #219;
diff --git a/polygerrit-ui/app/styles/themes/dark-theme.html b/polygerrit-ui/app/styles/themes/dark-theme.html
index ceb42a9..69a787e 100644
--- a/polygerrit-ui/app/styles/themes/dark-theme.html
+++ b/polygerrit-ui/app/styles/themes/dark-theme.html
@@ -105,6 +105,8 @@
       --light-rebased-add-highlight-color: #487165;
       --light-remove-add-highlight-color: #2f3f2f;
       --light-remove-highlight-color: #320404;
+      --coverage-covered: #e0f2f1;
+      --coverage-not-covered: #ffd1a4;
 
       /* syntax colors */
       --syntax-attr-color: #80cbbf;