Fix border for above buttons

Change-Id: I9248130c88bb89df096d12a295a8b96b468fbea9
diff --git a/polygerrit-ui/app/elements/diff/gr-context-controls/gr-context-controls.ts b/polygerrit-ui/app/elements/diff/gr-context-controls/gr-context-controls.ts
index dec5111..3b361ff 100644
--- a/polygerrit-ui/app/elements/diff/gr-context-controls/gr-context-controls.ts
+++ b/polygerrit-ui/app/elements/diff/gr-context-controls/gr-context-controls.ts
@@ -161,7 +161,7 @@
     .aboveButton {
       /* Display over preceding content / background placeholder. */
       transform: translateY(-100%);
-      border-bottom-width: 1px;
+      border-bottom-width: 0;
       border-bottom-right-radius: 0;
       border-bottom-left-radius: 0;
       padding: var(--spacing-xxs) var(--spacing-l);