[June 28] Dark high contrast theme (#20167)

* add beta note and mention using high contrast theme

* update screenshots

* add feature preview note to step

* update settings menu item

* update language

* use full theme name

* Apply suggestions from code review

Co-authored-by: Matt Pollard <mattpollard@users.noreply.github.com>

* version text

* version screenshots too

* build

* move beta callout below

Co-authored-by: Matt Pollard <mattpollard@users.noreply.github.com>
Co-authored-by: Leona B. Campbell <3880403+runleonarun@users.noreply.github.com>

content/github/setting-up-and-managing-your-github-user-account/managing-user-account-settings/managing-your-theme-settings.md

@@ -9,18 +9,27 @@ redirect_from:
   - /github/setting-up-and-managing-your-github-user-account/managing-your-theme-settings
 shortTitle: Manage theme settings
 ---
-For choice and flexibility in how and when you use {% data variables.product.product_name %}, you can configure theme settings to change how {% data variables.product.product_name %} looks to you. You can choose from themes that are light or dark, or you can configure {% data variables.product.product_name %} to follow your system settings. You may want to use a dark theme to reduce power consumption on certain devices, to reduce eye strain in low-light conditions, or because you prefer how the theme looks.
+
+For choice and flexibility in how and when you use {% data variables.product.product_name %}, you can configure theme settings to change how {% data variables.product.product_name %} looks to you. You can choose from themes that are light or dark, or you can configure {% data variables.product.product_name %} to follow your system settings.
+
+You may want to use a dark theme to reduce power consumption on certain devices, to reduce eye strain in low-light conditions, or because you prefer how the theme looks.{% ifversion fpt or ghae-issue-4618 %} People with visual impairment may benefit from the dark high contrast theme, with greater contrast between foreground and background elements.{% endif %}
+
+{% ifversion fpt %}{% note %}
+
+**Note:** The dark high contrast theme is currently available as a public beta. You can enable the dark high contrast theme using feature preview. For more information, see "[Exploring beta releases with feature preview](/get-started/using-github/exploring-early-access-releases-with-feature-preview#exploring-beta-releases-with-feature-preview)."
+
+{% endnote %}{% endif %}
 
 {% data reusables.user_settings.access_settings %}
 1. In the user settings sidebar, click **Appearance**.
     !["Appearance" tab in user settings sidebar](/assets/images/help/settings/appearance-tab.png)
 1. Under "Theme mode", select the drop-down menu, then click a theme preference.
     ![Drop-down menu under "Theme mode" for selection of theme preference](/assets/images/help/settings/theme-mode-drop-down-menu.png)
-1. Click the theme you'd like to use.
+1. Click the theme you'd like to use.{% ifversion fpt %} If you'd like to use the dark high contrast theme, you must enable the theme in feature preview. For more information, see "[Exploring beta releases with feature preview](/get-started/using-github/exploring-early-access-releases-with-feature-preview#exploring-beta-releases-with-feature-preview)."{% endif %}
     - If you chose a single theme, click a theme.
-      ![Radio buttons for the choice of a single theme](/assets/images/help/settings/theme-choose-a-single-theme.png)
+      {% ifversion fpt or ghae-issue-4618 %}![Radio buttons for the choice of a single theme](/assets/images/help/settings/theme-choose-a-single-theme-highcontrast.png){% else %}![Radio buttons for the choice of a single theme](/assets/images/help/settings/theme-choose-a-single-theme.png){% endif %}
     - If you chose to follow your system settings, click a day theme and a night theme.
-      ![Buttons for the choice of a theme to sync with the system setting](/assets/images/help/settings/theme-choose-a-day-and-night-theme-to-sync.png)
+      {% ifversion fpt or ghae-issue-4618 %}![Buttons for the choice of a theme to sync with the system setting](/assets/images/help/settings/theme-choose-a-day-and-night-theme-to-sync-highcontrast.png){% else %}![Buttons for the choice of a theme to sync with the system setting](/assets/images/help/settings/theme-choose-a-day-and-night-theme-to-sync.png){% endif %}
 
 ## Further reading