[NTP cleanup] Remove 'default-theme' and 'dark' classes.

Bug: None
Change-Id: I8ad45d279b2e649c6f2a19400367605d6cbfe693
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1811964Reviewed-by: Kristi Park <kristipark@chromium.org>
Commit-Queue: Gayane Petrosyan <gayane@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697855}

chrome/browser/resources/local_ntp/local_ntp.css

@@ -539,7 +539,7 @@ body.fakebox-focused #fakebox-cursor {
 }
 
 @media (prefers-color-scheme: dark) {
-  body:not(.light-chip) .default-theme.dark #mv-msg {
+  body:not(.light-chip) #mv-msg {
     color: rgb(var(--GG200-rgb));
   }
 }

chrome/browser/resources/local_ntp/local_ntp.js

@@ -72,8 +72,6 @@ const CLASSES = {
   CLOCK_ICON: 'clock-icon',
   // Applies styles to dialogs used in customization.
   CUSTOMIZE_DIALOG: 'customize-dialog',
-  DARK: 'dark',
-  DEFAULT_THEME: 'default-theme',
   DELAYED_HIDE_NOTIFICATION: 'mv-notice-delayed-hide',
   // Extended and elevated style for customization entry point.
   ENTRY_POINT_ENHANCED: 'ep-enhanced',
@@ -1390,8 +1388,6 @@ function renderTheme() {
     return;
   }
 
-  $(IDS.NTP_CONTENTS).classList.toggle(CLASSES.DARK, info.isNtpBackgroundDark);
-
   // Update dark mode styling.
   isDarkModeEnabled = window.matchMedia('(prefers-color-scheme: dark)').matches;
   document.body.classList.toggle('light-chip', !getUseDarkChips(info));
@@ -1585,9 +1581,6 @@ function setCustomThemeStyle(themeInfo) {
     mvxFilter = 'drop-shadow(0 0 0 ' + textColor + ')';
   }
 
-  $(IDS.NTP_CONTENTS)
-      .classList.toggle(CLASSES.DEFAULT_THEME, themeInfo.usingDefaultTheme);
-
   document.body.style.setProperty('--text-color', textColor);
   document.body.style.setProperty('--text-color-light', textColorLight);
 }