[CrOS MultiDevice] Sync setup flow font color with mocks

Note that there will be a separate CL with password page formatting
because it requires some additional tweaks.

Specs:
https://drive.google.com/file/d/1UqHV67OrdGT0_G0L98nV5IVr26OkHu9F/view?usp=sharing

New change screenshots:
Start Setup Page: http://screen/1PkWGgTYmVG
Setup Complete Page: http://screen/drwnruTOBNw

Bug: 878646, 878644
Change-Id: Idf2afceb75dbb1c5b0157ffd8405fceea59cff46
Reviewed-on: https://chromium-review.googlesource.com/1246781Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Jordy Greenblatt <jordynass@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594468}

ui/webui/resources/cr_components/chromeos/multidevice_setup/multidevice_setup.html

@@ -18,6 +18,7 @@
       :host {
         @apply --layout-vertical;
         box-sizing: border-box;
+        color: var(--google-grey-700);
         height: 100%;
         padding: 60px 64px 32px 64px;
       }

ui/webui/resources/cr_components/chromeos/multidevice_setup/start_setup_page.html

@@ -31,6 +31,10 @@
         width: 320px;
       }
 
+      #deviceSelectionContainer {
+        color: var(--paper-grey-600);
+      }
+
       #feature-details-container {
         border-left: 1px solid rgb(218, 220, 224);
         padding-left: 24px;
@@ -56,12 +60,17 @@
       .feature-detail span {
         padding-left: 28px;
       }
+
+      #footnote {
+        color: var(--paper-grey-600);
+      }
     </style>
+
     <ui-page header-text="[[headerText]]" icon-name="google-g">
       <span slot="message" inner-h-t-m-l="[[messageHtml]]"></span>
       <div slot="additional-content">
         <div id="selector-and-details-container">
-          <div class="flex">
+          <div id="deviceSelectionContainer" class="flex">
             [[getDeviceSelectionHeader_(devices)]]
             <div class="flex"></div>
             <div hidden$="[[!doesDeviceListHaveOneElement_(devices)]]">

ui/webui/resources/cr_components/chromeos/multidevice_setup/ui_page.html

@@ -13,7 +13,7 @@
       }
 
       h1 {
-        color: rgb(32, 33, 36);
+        color: var(--google-grey-900);
         font-family: 'Google Sans';
         font-size: 28px;
         line-height: 28px;