Use border instead of fill in suggestion chips in the reply dialog

Change-Id: Ib9b8da89ad74e33634d7dc00ed3c8ffe4d059720
diff --git a/ui/suggest-owners.js b/ui/suggest-owners.js
index bcfb2ef..0212224 100644
--- a/ui/suggest-owners.js
+++ b/ui/suggest-owners.js
@@ -178,13 +178,13 @@
           height: 16px;
         }
         gr-account-label {
-          background-color: var(--background-color-tertiary);
           display: inline-block;
           padding: var(--spacing-xs) var(--spacing-m);
           user-select: none;
           border: 1px solid transparent;
           --label-border-radius: 8px;
           --account-max-length: 100px;
+          border: 1px solid var(--border-color);
         }
         gr-account-label:focus {
           outline: none;