Make gr-account-chip use chip-background-color

Mistakenly not used in e46284e4.

Change-Id: Ib5947e1d2e89fe79693d79eb16ba1319cf1b100d

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

diff --git a/polygerrit-ui/app/elements/shared/gr-account-chip/gr-account-chip.html b/polygerrit-ui/app/elements/shared/gr-account-chip/gr-account-chip.html
index 8a86f93..89ab8fe 100644
--- a/polygerrit-ui/app/elements/shared/gr-account-chip/gr-account-chip.html
+++ b/polygerrit-ui/app/elements/shared/gr-account-chip/gr-account-chip.html
@@ -31,7 +31,7 @@
       }
       .container {
         align-items: center;
-        background: var(--table-header-background-color);
+        background: var(--chip-background-color);
         border-radius: .75em;
         display: inline-flex;
         padding: 0 .5em;