Nux onboarding: fix precedence of styling

Make css selectors more specific so that it works both in polymer 1 and 2.

Bug: 874151
Change-Id: Ie39ea7a9a919b5d627491ba8b8d301720aa2cc32
Reviewed-on: https://chromium-review.googlesource.com/c/1287266Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Scott Chen <scottchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600898}

chrome/browser/resources/welcome/onboarding_welcome/email/nux_email.html

@@ -6,16 +6,6 @@
 <dom-module id="nux-email">
   <template>
     <style>
-      :host-context(#viewManager):host([slot='view']) {
-        /* Unsets cr-view-manager's styling to make all views full-page, and
-           allows the content to be centered horizontally/vertically on the
-           page. */
-        bottom: initial;
-        left: initial;
-        right: initial;
-        top: initial;
-      }
-
       .email-ask {
         text-align: center;
       }

chrome/browser/resources/welcome/onboarding_welcome/google_apps/nux_google_apps.html

@@ -10,16 +10,6 @@
 <dom-module id="nux-google-apps">
   <template>
     <style include="paper-button-style">
-      :host-context(#viewManager):host([slot='view']) {
-        /* Unsets cr-view-manager's styling to make all views full-page, and
-           allows the content to be centered horizontally/vertically on the
-           page. */
-        bottom: initial;
-        left: initial;
-        right: initial;
-        top: initial;
-      }
-
       .apps-ask {
         margin-left: auto;
         margin-right: auto;

chrome/browser/resources/welcome/onboarding_welcome/set_as_default/nux_set_as_default.html

@@ -11,16 +11,6 @@
 <dom-module id="nux-set-as-default">
   <template>
     <style include="paper-button-style">
-      :host-context(#viewManager):host([slot='view']) {
-        /* Unsets cr-view-manager's styling to make all views full-page, and
-           allows the content to be centered horizontally/vertically on the
-           page. */
-        bottom: initial;
-        left: initial;
-        right: initial;
-        top: initial;
-      }
-
       .container {
         text-align: center;
         width: 800px;

chrome/browser/resources/welcome/onboarding_welcome/welcome_app.html

@@ -20,6 +20,15 @@
         margin: 0;
         min-height: 100vh;
       }
+
+      #viewManager :-webkit-any(nux-email,
+          nux-google-apps, nux-set-as-default) {
+        /* Override cr-view-manager's default styling for view. */
+        bottom: initial;
+        left: initial;
+        right: initial;
+        top: initial;
+      }
     </style>
     <cr-view-manager id="viewManager">
       <landing-view id="step-landing" slot="view" class="active"></landing-view>