DevTools: polish event listeners pane UI.

Source/devtools/front_end/components/eventListenersView.css

Index: Source/devtools/front_end/components/eventListenersView.css
diff --git a/Source/devtools/front_end/components/eventListenersView.css b/Source/devtools/front_end/components/eventListenersView.css
index 078a290f0061dbc858dc618a262fcf26218a99ac..48bea5a023fbf27035d371b8ccb0e934a35f379f 100644
--- a/Source/devtools/front_end/components/eventListenersView.css
+++ b/Source/devtools/front_end/components/eventListenersView.css
@@ -13,7 +13,7 @@
 }
 
 .event-listener-tree > li {
-    border-top: 1px solid rgb(231, 231, 231);
+    border-top: 1px solid #f0f0f0;
 }
 
 .event-listener-tree > li:first-of-type {
@@ -22,6 +22,7 @@
 
 .event-listener-tree {
     padding-left: 0 !important;
+    padding-right: 3px;
 }
 
 .event-listener-tree li.parent::before {
@@ -34,4 +35,4 @@
 
 .event-listener-tree-subtitle {
     float: right;
-}
+}