diff --git a/__tests__/component/Viewer.spec.ts b/__tests__/component/Viewer.spec.ts
index b4c364f..02c5ee9 100644
--- a/__tests__/component/Viewer.spec.ts
+++ b/__tests__/component/Viewer.spec.ts
@@ -119,17 +119,31 @@ describe('Viewer.open()', () => {
 		expect(modalProps().show).toBe(true)
 	})
 
-	it.each([
-		['light', true],
-		['dark', false],
-		['default', false],
-	] as const)('gives the modal a light backdrop only for a %s themed handler', async (theme, lightBackdrop) => {
-		const handler = makeHandler({ id: theme, tagName: `oca-viewer-${theme}`, theme, enabled: () => true })
-		const { vm, wrapper, modalProps } = mountViewer([handler])
-		const f1 = makeFile()
-		await vm.open([f1], f1)
-		await wrapper.vm.$nextTick()
-		expect(modalProps().lightBackdrop).toBe(lightBackdrop)
+	describe('under the user\'s theme', () => {
+		afterEach(() => document.body.style.removeProperty('--background-invert-if-dark'))
+
+		// The theme the user runs, the one a handler asks for, then whether the
+		// backdrop is light and whether it takes the theme's colours
+		it.each([
+			['light', 'light', true, false],
+			['light', 'dark', false, false],
+			['light', 'default', true, true],
+			['light', undefined, false, false],
+			['dark', 'light', true, false],
+			['dark', 'dark', false, false],
+			['dark', 'default', false, true],
+			['dark', undefined, false, false],
+		] as const)('a %s theme gives a %s themed handler a light backdrop: %s, the theme\'s colours: %s', async (userTheme, theme, lightBackdrop, followsTheme) => {
+			document.body.style.setProperty('--background-invert-if-dark', userTheme === 'dark' ? 'invert(100%)' : 'no')
+			const id = theme ?? 'unset'
+			const handler = makeHandler({ id, tagName: `oca-viewer-${id}`, theme, enabled: () => true })
+			const { vm, wrapper, modalProps } = mountViewer([handler])
+			const f1 = makeFile()
+			await vm.open([f1], f1)
+			await wrapper.vm.$nextTick()
+			expect(modalProps().lightBackdrop).toBe(lightBackdrop)
+			expect(wrapper.find('.nc-modal-stub').classes('viewer__modal--default')).toBe(followsTheme)
+		})
 	})
 })
 
diff --git a/__tests__/component/mountViewer.ts b/__tests__/component/mountViewer.ts
index 69f7efd..840f17f 100644
--- a/__tests__/component/mountViewer.ts
+++ b/__tests__/component/mountViewer.ts
@@ -17,9 +17,9 @@ import { registerTestHandlers } from '../factories.ts'
  * Minimal NcModal stub.
  *
  * It renders the default slot and the `#actions` slot so we can assert on the
- * handler custom-element markup and drive the header actions. The style is
- * kept, as the real modal applies it: that is how the viewer makes room for
- * the sidebar. Navigation is
+ * handler custom-element markup and drive the header actions. The style and
+ * classes are kept, as the real modal applies them: that is how the viewer
+ * makes room for the sidebar and themes itself. Navigation is
  * driven from tests through `findComponent(NcModalStub).vm.$emit('next'|'previous'|'close')`.
  * The relevant props (`name`, `show`, `hasNext`, `hasPrevious`, `isComparing`
  * related flags) are declared so they can be read back via `.props()`.
@@ -45,6 +45,7 @@ export const NcModalStub = defineComponent({
 		<div
 			v-show="show"
 			class="nc-modal-stub"
+			:class="$attrs.class"
 			:style="$attrs.style"
 			:data-handler="$attrs['data-handler']"
 			:data-name="name"
diff --git a/e2e/theme.spec.ts b/e2e/theme.spec.ts
index 8cca883..43ca013 100644
--- a/e2e/theme.spec.ts
+++ b/e2e/theme.spec.ts
@@ -45,4 +45,17 @@ test.describe('Backdrop', () => {
 		// What WCAG asks of normal text
 		expect(contrast).toBeGreaterThanOrEqual(4.5)
 	})
+
+	// The dark palette was set on the whole modal, so it reached into what a
+	// handler shows: a document in Text came out white on black under a
+	// light theme, and printed grey
+	test('leaves the colours of what a handler shows to the theme', async ({ page }) => {
+		const viewer = new ViewerPage(page)
+		await viewer.open('photo.jpg')
+		await viewer.waitForOpen()
+
+		const text = (selector: string) => page.locator(selector).first().evaluate((element) => getComputedStyle(element).getPropertyValue('--color-main-text').trim())
+		expect(await text('.viewer__modal .modal-header')).toBe('#ffffff')
+		expect(await text('.viewer__modal oca-viewer-image')).not.toBe('#ffffff')
+	})
 })
diff --git a/lib/handlers.ts b/lib/handlers.ts
index f6c4265..c4aa044 100644
--- a/lib/handlers.ts
+++ b/lib/handlers.ts
@@ -94,7 +94,8 @@ export interface IHandler {
 	onInit?: () => Promise<void>
 
 	/**
-	 * Viewer modal theme (one of 'dark', 'light', 'default')
+	 * Viewer modal theme: 'dark' (the default), 'light', or 'default' to
+	 * follow the user's theme
 	 */
 	theme?: 'dark' | 'light' | 'default'
 
diff --git a/lib/views/Viewer.vue b/lib/views/Viewer.vue
index d376ddc..cd0cb11 100644
--- a/lib/views/Viewer.vue
+++ b/lib/views/Viewer.vue
@@ -25,6 +25,7 @@
 		:slideshowPaused="slideshowPaused"
 		:spreadNavigation="true"
 		:style="{ width: isSidebarShown ? `${sidebarPosition}px` : null }"
+		:class="{ 'viewer__modal--default': followsTheme }"
 		class="viewer__modal"
 		size="full"
 		@close="close"
@@ -147,6 +148,7 @@
 		<!-- Error message -->
 		<NcEmptyContent
 			v-else-if="errorString"
+			class="viewer__error"
 			:name="errorString"
 			:description="t('We were unable to display the requested file.')">
 			<template #icon>
@@ -353,6 +355,8 @@ const canSwipe = ref(true)
 const isFullscreen = ref(false)
 const editing = ref(false)
 const lightBackdrop = ref(false)
+// The handler asked for the user's own theme, backdrop and header included
+const followsTheme = ref(false)
 const slideshowRunning = ref(false)
 // Whether the current handler is playing media, which the slideshow waits for
 const playing = ref(false)
@@ -1157,13 +1161,22 @@ const compare: ViewerAPI['compare'] = async (file1, file2, handlerId) => {
 /**
  * Handle Viewer opening to determine backdrop style.
  *
- * The viewer is dark whatever theme the user runs: a photo or a video reads
- * better against dark, and the room around it should not compete with it.
- * A handler showing something else — a document, say — can ask for a light
- * backdrop instead, but nothing follows the user's theme here.
+ * The viewer is dark unless the handler asks otherwise: a photo or a video
+ * reads better against dark, and the room around it should not compete with
+ * it. A handler showing something else, a document say, can ask for a light
+ * backdrop, or for the user's own theme with 'default'.
  */
 function onOpen() {
-	lightBackdrop.value = (currentHandler.value?.theme ?? 'default') === 'light'
+	const theme = currentHandler.value?.theme ?? 'dark'
+	followsTheme.value = theme === 'default'
+	lightBackdrop.value = theme === 'light' || (followsTheme.value && isThemeLight())
+}
+
+/**
+ * Whether the user runs a light theme, the way the server's own styles tell.
+ */
+function isThemeLight(): boolean {
+	return getComputedStyle(document.body).getPropertyValue('--background-invert-if-dark').trim() !== 'invert(100%)'
 }
 
 /**
@@ -1734,17 +1747,32 @@ defineExpose<ViewerAPI>({
 
 <style scoped lang="scss">
 .viewer__modal {
-	// The backdrop is dark whatever theme the server runs, so what sits on
-	// it has to come from the dark palette too. Without this the header
-	// inherits the light theme's #222 and lands at 1.3:1 against black,
-	// which is a title nobody can read. A handler that asked for a light
-	// backdrop keeps the theme's own colours.
-	&:not(.modal-mask--light) {
-		--color-main-text: #ffffff;
-		--color-text-maxcontrast: #d8d8d8;
-		--color-main-background: #171717;
-
-		color: var(--color-main-text);
+	// The backdrop is dark whatever theme the server runs, so what the
+	// viewer itself puts on it has to come from the dark palette too.
+	// Without this the header inherits the light theme's #222 and lands at
+	// 1.3:1 against black, which is a title nobody can read. Only the
+	// viewer's own parts: a handler's content keeps the theme's colours, or
+	// a document shown by Text turns dark under a light theme. A handler
+	// that asked for a light backdrop or for the user's theme keeps them
+	// everywhere.
+	&:not(.modal-mask--light, .viewer__modal--default) {
+		:deep(.modal-header),
+		:deep(.prev),
+		:deep(.next),
+		:deep(.modal-container__close),
+		.viewer__loading,
+		.viewer__error {
+			--color-main-text: #ffffff;
+			--color-text-maxcontrast: #d8d8d8;
+			--color-main-background: #171717;
+
+			color: var(--color-main-text);
+		}
+	}
+
+	// Over NcModal's translucent black or white backdrop
+	&--default {
+		background-color: var(--color-main-background) !important;
 	}
 
 	:deep(.modal-container__content) {