Safe browsing intersititials - Update fixed nav background colour

Bug: 834899
Change-Id: I9bcbcda4b121d8c732f808e0745b8b33a1da647f
Reviewed-on: https://chromium-review.googlesource.com/1043872Reviewed-by: Adrienne Porter Felt <felt@chromium.org>
Commit-Queue: Edward Jung <edwardjung@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556273}

components/security_interstitials/core/common/resources/interstitial_common.css

@@ -268,9 +268,9 @@ input[type=checkbox]:checked ~ .checkbox::before {
        (min-width: 421px) and (min-height: 240px) and
        (max-height: 560px) {
   body .nav-wrapper {
-    background: #f7f7f7;
+    background: #fff;
     bottom: 0;
-    box-shadow: 0 -22px 40px rgb(247, 247, 247);
+    box-shadow: 0 -22px 40px #fff;
     left: 0;
     margin: 0 auto;
     max-width: 736px;