Replace #eee with header-background-color

Change-Id: I17bb95f92129afd3f2528f5e52462d1c56ad7a1f

polygerrit-ui/app/elements/change/gr-included-in-dialog/gr-included-in-dialog.html

@@ -59,7 +59,7 @@ limitations under the License.
       }
       ul li {
         border-radius: .2em;
-        background: #eee;
+        background: var(--header-background-color);
         display: inline-block;
         margin: 0 .2em .4em .2em;
         padding: .2em .4em;

polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html

@@ -62,7 +62,7 @@ limitations under the License.
         table-layout: fixed;
       }
       .lineNum {
-        background-color: #eee;
+        background-color: var(--header-background-color);
       }
       .image-diff .gr-diff {
         text-align: center;
@@ -211,7 +211,7 @@ limitations under the License.
         display: block;
       }
       .target-row td.blame {
-        background: #eee;
+        background: var(--header-background-color);
       }
       col.blame {
         display: none;

polygerrit-ui/app/elements/shared/gr-account-chip/gr-account-chip.html

@@ -31,7 +31,7 @@ limitations under the License.
       }
       .container {
         align-items: center;
-        background: #eee;
+        background: var(--header-background-color);
         border-radius: .75em;
         display: inline-flex;
         padding: 0 .5em;

polygerrit-ui/app/elements/shared/gr-linked-chip/gr-linked-chip.html

@@ -31,7 +31,7 @@ limitations under the License.
       }
       .container {
         align-items: center;
-        background: #eee;
+        background: var(--header-background-color);
         border-radius: .75em;
         display: inline-flex;
         padding: 0 .5em;