improve(ui): alignment of toggle right sidebar icon

src/main/frontend/components/header.css

@@ -27,10 +27,10 @@
   }
 
   > .r {
-    @apply pr-4;
     align-items: center;
     flex: 1;
     justify-content: flex-end;
+    padding-right: 6px;
   }
 
   /* To prevent header glitch on Safari */
@@ -201,7 +201,7 @@
 }
 
 .button.icon {
-  @apply w-8 h-8 p-1;
+  @apply w-8 h-8 p-1 flex items-center justify-center;
 }
 
 .button.icon.add-graph-btn {