tooltips: Fix offscreen tooltips taking scroll space.

web/styles/tooltips.css

@@ -87,4 +87,20 @@
         text-align: center;
         line-height: 14px;
     }
+
+    /* If the reference of the tooltip is went offscreen while scrolling,
+       the tooltip will be visible until the scrolling stops. Popper adds
+       `data-reference-hidden` attribute to those tooltips whole reference is
+       hidden. Since tooltips have `absolute` position, they can occupy scroll
+       space offscreen and cause document to have the wrong scroll height.
+       Setting `display: none` makes sure it doesn't occupy any offscreen space.
+
+       NOTE: This data attribtute has changed each time in the past 3 releases and
+       if we upgrade tippy from v6, we should check if this attribute is still valid.
+
+       See https://github.com/atomiks/tippyjs/issues/555 for some discussion on this.
+    */
+    [data-reference-hidden] {
+        display: none;
+    }
 }