diff --git a/apps/theming/lib/Service/ThemesService.php b/apps/theming/lib/Service/ThemesService.php
index 8244e69e21911..d7127173848bb 100644
--- a/apps/theming/lib/Service/ThemesService.php
+++ b/apps/theming/lib/Service/ThemesService.php
@@ -170,12 +170,15 @@ public function isEnabled(ITheme $theme): bool {
 	 * @return string[]
 	 */
 	public function getEnabledThemes(): array {
+		$enforcedTheme = $this->config->getSystemValueString('enforce_theme', '');
 		$user = $this->userSession->getUser();
 		if ($user === null) {
+			if ($enforcedTheme !== '') {
+				return [$enforcedTheme];
+			}
 			return [];
 		}
 
-		$enforcedTheme = $this->config->getSystemValueString('enforce_theme', '');
 		$enabledThemes = json_decode($this->config->getUserValue($user->getUID(), Application::APP_ID, 'enabled-themes', '["default"]'));
 		if ($enforcedTheme !== '') {
 			return array_merge([$enforcedTheme], $enabledThemes);
diff --git a/core/templates/layout.guest.php b/core/templates/layout.guest.php
index 5ebada9293403..363fe9dde2628 100644
--- a/core/templates/layout.guest.php
+++ b/core/templates/layout.guest.php
@@ -25,7 +25,9 @@
 		<?php emit_script_loading_tags($_); ?>
 		<?php print_unescaped($_['headers']); ?>
 	</head>
-	<body id="<?php p($_['bodyid']);?>">
+	<body id="<?php p($_['bodyid']);?>" <?php foreach ($_['enabledThemes'] as $themeId) {
+		p("data-theme-$themeId ");
+	}?> data-themes="<?php p(join(',', $_['enabledThemes'])) ?>">
 		<?php include 'layout.noscript.warning.php'; ?>
 		<?php foreach ($_['initialStates'] as $app => $initialState) { ?>
 			<input type="hidden" id="initial-state-<?php p($app); ?>" value="<?php p(base64_encode($initialState)); ?>">
diff --git a/core/templates/layout.public.php b/core/templates/layout.public.php
index 81b384987b8f8..8743554226961 100644
--- a/core/templates/layout.public.php
+++ b/core/templates/layout.public.php
@@ -26,11 +26,13 @@
 	<?php emit_script_loading_tags($_); ?>
 	<?php print_unescaped($_['headers']); ?>
 </head>
-<body id="<?php p($_['bodyid']);?>">
-<?php include('layout.noscript.warning.php'); ?>
-<?php foreach ($_['initialStates'] as $app => $initialState) { ?>
-	<input type="hidden" id="initial-state-<?php p($app); ?>" value="<?php p(base64_encode($initialState)); ?>">
-<?php }?>
+<body id="<?php p($_['bodyid']);?>" <?php foreach ($_['enabledThemes'] as $themeId) {
+	p("data-theme-$themeId ");
+}?> data-themes="<?php p(join(',', $_['enabledThemes'])) ?>">
+	<?php include('layout.noscript.warning.php'); ?>
+	<?php foreach ($_['initialStates'] as $app => $initialState) { ?>
+		<input type="hidden" id="initial-state-<?php p($app); ?>" value="<?php p(base64_encode($initialState)); ?>">
+	<?php }?>
 	<div id="skip-actions">
 		<?php if ($_['id-app-content'] !== null) { ?><a href="<?php p($_['id-app-content']); ?>" class="button primary skip-navigation skip-content"><?php p($l->t('Skip to main content')); ?></a><?php } ?>
 		<?php if ($_['id-app-navigation'] !== null) { ?><a href="<?php p($_['id-app-navigation']); ?>" class="button primary skip-navigation"><?php p($l->t('Skip to navigation of app')); ?></a><?php } ?>
diff --git a/lib/private/TemplateLayout.php b/lib/private/TemplateLayout.php
index cb2678acce41d..5d29b06a73b8f 100644
--- a/lib/private/TemplateLayout.php
+++ b/lib/private/TemplateLayout.php
@@ -183,6 +183,8 @@ public function __construct($renderAs, $appId = '') {
 			if ($user) {
 				$userDisplayName = $user->getDisplayName();
 			}
+			$theme = $this->config->getSystemValueString('enforce_theme', '');
+			$this->assign('enabledThemes', $theme === '' ? [] : [$theme]);
 			$this->assign('user_displayname', $userDisplayName);
 			$this->assign('user_uid', \OC_User::getUser());
 		} elseif ($renderAs === TemplateResponse::RENDER_AS_PUBLIC) {
@@ -190,6 +192,14 @@ public function __construct($renderAs, $appId = '') {
 			$this->assign('appid', $appId);
 			$this->assign('bodyid', 'body-public');
 
+			// Set body data-theme
+			$this->assign('enabledThemes', []);
+			if ($this->appManager->isEnabledForUser('theming') && class_exists('\OCA\Theming\Service\ThemesService')) {
+				/** @var \OCA\Theming\Service\ThemesService $themesService */
+				$themesService = \OC::$server->get(\OCA\Theming\Service\ThemesService::class);
+				$this->assign('enabledThemes', $themesService->getEnabledThemes());
+			}
+
 			// Set logo link target
 			$logoUrl = $this->config->getSystemValueString('logo_url', '');
 			$this->assign('logoUrl', $logoUrl);
