Inherit default text color from MainTheme.

chrome/android/java/res/layout/payment_request_header.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright 2016 The Chromium Authors. All rights reserved.
      Use of this source code is governed by a BSD-style license that can be
      found in the LICENSE file. -->
 
 <!-- Header containing information about the site.
      Java code inflating this layout manages the hiding and adjustment of elements in the layout.
      Request dialog: Displays an X in the top right corner, allowing the user to close it.
      Result dialog:  Displays no X.  Title goes all the way to the end.
 -->
@@ skipping 20 matching lines @@
             android:layout_height="wrap_content"
             android:layout_width="wrap_content"
             android:layout_marginStart="56dp"
             android:layout_marginEnd="56dp"
             android:layout_marginBottom="@dimen/payments_section_vertical_spacing"
             android:layout_marginTop="@dimen/payments_section_vertical_spacing"
             android:layout_gravity="center_vertical"
             android:orientation="vertical">
 
             <TextView
+                style="@style/PaymentsUiSectionDefaultText"
                 android:id="@+id/page_title"
                 android:layout_height="wrap_content"
                 android:layout_width="wrap_content"
                 android:ellipsize="end"
                 android:maxLines="1"
                 android:singleLine="true"
-                android:textColor="@color/default_text_color"
-                android:textSize="16sp"
                 android:textStyle="bold" />
 
             <TextView
                 android:id="@+id/hostname"
                 android:layout_height="wrap_content"
                 android:layout_width="wrap_content"
                 android:ellipsize="start"
                 android:maxLines="1"
                 android:singleLine="true"
                 android:textColor="@color/descriptive_text_color"
                 android:textSize="14sp" />
         </LinearLayout>
 
         <ImageView
             android:id="@+id/close_button"
             android:layout_gravity="end|center_vertical"
             android:layout_height="56dp"
             android:layout_width="56dp"
             android:src="@drawable/btn_close"
             android:contentDescription="@string/close"
             android:background="?attr/selectableItemBackground"
             android:scaleType="center" />
     </FrameLayout>
 
 </merge>