ChromeOS OOBE: Implement network selection screen "Back" button.

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 5c9eb56354bcfcd438ec729cf9ac8ad7278ba173..0e905a4838b9cf1a3310588341b8929cdccd987f 100644
--- a/chrome/browser/resources/chromeos/login/oobe_welcome.css
+++ b/chrome/browser/resources/chromeos/login/oobe_welcome.css
@@ -18,6 +18,10 @@
   font: 13px Roboto, sans-serif;
 }
 
+#languageScreen .bottom-buttons {
+  padding: 0 24px;
+}
+
 /************* Accessibility Screen **************/
 #accessibilityScreen oobe-a11y-option {
   border-top: 1px solid lightgrey;
@@ -27,3 +31,12 @@
 #accessibilityScreen oobe-a11y-option:last-of-type {
   border-bottom: 1px solid rgba(0, 0, 0, 0.14);
 }
+
+#accessibilityScreen .bottom-buttons {
+  padding: 0 24px;
+}
+
+/************* Accessibility Screen **************/
+#networkSelectionScreen .bottom-buttons {
+  padding: 0 6px; /* = 8px - 2px back button border */
+}