ChromeOS OOBE: Update Welcome screen colors after UI review.

chrome/browser/resources/chromeos/login/oobe_welcome.css

Index: chrome/browser/resources/chromeos/login/oobe_welcome.css
diff --git a/chrome/browser/resources/chromeos/login/oobe_welcome.css b/chrome/browser/resources/chromeos/login/oobe_welcome.css
index 034843045718a6a3f120cfd3eb852994556becc7..6f01d3f37a95c4d2089499679e8545947a49cbae 100644
--- a/chrome/browser/resources/chromeos/login/oobe_welcome.css
+++ b/chrome/browser/resources/chromeos/login/oobe_welcome.css
@@ -2,15 +2,19 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file. */
 
+:root {
+  --oobe-dialog-list-item-border: 1px solid rgba(0, 0, 0, 0.06);
+}
+
 /************* Language Screen **************/
 #languageScreen .language-selection-entry {
-  border-top: 1px solid lightgrey;
+  border-top: var(--oobe-dialog-list-item-border);
   height: 44px;
   padding: 0 10px;
 }
 
 #languageScreen .language-selection-entry:last-of-type {
-  border-bottom: 1px solid lightgrey;
+  border-bottom: var(--oobe-dialog-list-item-border);
 }
 
 #languageScreen .language-selection-title {
@@ -24,12 +28,12 @@
 
 /************* Accessibility Screen **************/
 #accessibilityScreen oobe-a11y-option {
-  border-top: 1px solid lightgrey;
+  border-top: var(--oobe-dialog-list-item-border);
   min-height: 56px;
 }
 
 #accessibilityScreen oobe-a11y-option:last-of-type {
-  border-bottom: 1px solid rgba(0, 0, 0, 0.14);
+  border-bottom: var(--oobe-dialog-list-item-border);
 }
 
 #accessibilityScreen .bottom-buttons {
@@ -47,13 +51,13 @@
 
 /************* Timezone Screen **************/
 #timezoneScreen .timezone-selection-entry {
-  border-top: 1px solid lightgrey;
+  border-top: var(--oobe-dialog-list-item-border);
   height: 44px;
   padding: 0 20px;
 }
 
 #timezoneScreen .timezone-selection-entry:last-of-type {
-  border-bottom: 1px solid lightgrey;
+  border-bottom: var(--oobe-dialog-list-item-border);
 }
 
 #timezoneScreen .timezone-selection-title {