From 95b859209f846857555798d5e17cc48ef643db41 Mon Sep 17 00:00:00 2001
From: Brian Vaughn <bvaughn@fb.com>
Date: Tue, 12 Feb 2019 21:09:33 -0500
Subject: [PATCH] Fixed NaN warning for pre-mount CSS prop read

---
 src/devtools/views/Tree.js | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/src/devtools/views/Tree.js b/src/devtools/views/Tree.js
index 2326415ec7..a696c815dd 100644
--- a/src/devtools/views/Tree.js
+++ b/src/devtools/views/Tree.js
@@ -79,12 +79,13 @@ export default function Tree(props: Props) {
     [baseDepth, numElements, getElementAtIndex]
   );
 
-  const itemSize = parseInt(
-    getComputedStyle((document.body: any)).getPropertyValue(
-      '--line-height-data'
-    ),
-    10
-  );
+  const itemSize =
+    parseInt(
+      getComputedStyle((document.body: any)).getPropertyValue(
+        '--line-height-data'
+      ),
+      10
+    ) || 18;
 
   return (
     <div className={styles.Tree}>