[NTP] HTML tag doesn't need background color.

HTML tag doesn't need background color as background color is applied
pn body.

theme.css adds background color to local_ntp HTML tag from theme
properties but doesn't get updated on theme change which results in
funky effects described in the bug.

Bug: 998482
Change-Id: Idbb6c7df15af029fdaa9e229ffa4889ce1ee02e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1775189
Commit-Queue: Gayane Petrosyan <gayane@chromium.org>
Reviewed-by: Dan Beam <dbeam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#691807}

chrome/browser/search/local_ntp_source.cc

@@ -307,7 +307,7 @@ std::string GetThemeCSS(Profile* profile) {
       ThemeService::GetThemeProviderForProfile(profile)
           .GetColor(ThemeProperties::COLOR_NTP_BACKGROUND);
 
-  return base::StringPrintf("html { background-color: #%02X%02X%02X; }",
+  return base::StringPrintf("body { background-color: #%02X%02X%02X; }",
                             SkColorGetR(background_color),
                             SkColorGetG(background_color),
                             SkColorGetB(background_color));