diff --git a/packages/core/rendering/core-rendering-server-internal/src/render_utils.test.ts b/packages/core/rendering/core-rendering-server-internal/src/render_utils.test.ts
index aefe6e2287e4f..96a81976c23ad 100644
--- a/packages/core/rendering/core-rendering-server-internal/src/render_utils.test.ts
+++ b/packages/core/rendering/core-rendering-server-internal/src/render_utils.test.ts
@@ -61,7 +61,6 @@ describe('getStylesheetPaths', () => {
             darkMode: true,
             themeVersion: 'v8',
             baseHref: '/base-path/buildShaShort',
-            buildNum: 17,
           })
         ).toMatchInlineSnapshot(`
           Array [
@@ -83,7 +82,6 @@ describe('getStylesheetPaths', () => {
             darkMode: false,
             themeVersion: 'v8',
             baseHref: '/base-path/buildShaShort',
-            buildNum: 69,
           })
         ).toMatchInlineSnapshot(`
           Array [
diff --git a/packages/core/rendering/core-rendering-server-internal/src/render_utils.ts b/packages/core/rendering/core-rendering-server-internal/src/render_utils.ts
index e8b9e8b76c5e8..f4ce68885ddb6 100644
--- a/packages/core/rendering/core-rendering-server-internal/src/render_utils.ts
+++ b/packages/core/rendering/core-rendering-server-internal/src/render_utils.ts
@@ -46,11 +46,7 @@ export const getScriptPaths = ({
   }
 };
 
-export const getCommonStylesheetPaths = ({
-  baseHref,
-}: {
-  baseHref: string;
-}) => {
+export const getCommonStylesheetPaths = ({ baseHref }: { baseHref: string }) => {
   const bundlesHref = getBundlesHref(baseHref);
   return [
     `${bundlesHref}/kbn-ui-shared-deps-src/${UiSharedDepsSrc.cssDistFilename}`,
@@ -62,11 +58,9 @@ export const getThemeStylesheetPaths = ({
   darkMode,
   themeVersion,
   baseHref,
-  buildNum,
 }: {
   darkMode: boolean;
   themeVersion: UiSharedDepsNpm.ThemeVersion;
-  buildNum: number;
   baseHref: string;
 }) => {
   const bundlesHref = getBundlesHref(baseHref);
diff --git a/packages/core/rendering/core-rendering-server-internal/src/rendering_service.tsx b/packages/core/rendering/core-rendering-server-internal/src/rendering_service.tsx
index a62780d058d1b..dcf7162b481f8 100644
--- a/packages/core/rendering/core-rendering-server-internal/src/rendering_service.tsx
+++ b/packages/core/rendering/core-rendering-server-internal/src/rendering_service.tsx
@@ -125,7 +125,6 @@ export class RenderingService {
       mode: this.coreContext.env.mode,
       packageInfo: this.coreContext.env.packageInfo,
     };
-    const buildNum = env.packageInfo.buildNum;
     const staticAssetsHrefBase = http.staticAssets.getHrefBase();
     const basePath = http.basePath.get(request);
     const { serverBasePath, publicBaseUrl } = http.basePath;
@@ -191,7 +190,6 @@ export class RenderingService {
         darkMode: mode,
         themeVersion,
         baseHref: staticAssetsHrefBase,
-        buildNum,
       });
     const commonStylesheetPaths = getCommonStylesheetPaths({
       baseHref: staticAssetsHrefBase,
diff --git a/packages/core/theme/core-theme-browser-internal/src/theme_service.ts b/packages/core/theme/core-theme-browser-internal/src/theme_service.ts
index 9871a25ee7eea..c02074be77c3b 100644
--- a/packages/core/theme/core-theme-browser-internal/src/theme_service.ts
+++ b/packages/core/theme/core-theme-browser-internal/src/theme_service.ts
@@ -6,8 +6,7 @@
  * Side Public License, v 1.
  */
 
-import { Subject, ReplaySubject } from 'rxjs';
-import { shareReplay, takeUntil } from 'rxjs/operators';
+import { of } from 'rxjs';
 import { _setDarkMode } from '@kbn/ui-theme';
 import type { InjectedMetadataTheme } from '@kbn/core-injected-metadata-common-internal';
 import type { InternalInjectedMetadataSetup } from '@kbn/core-injected-metadata-browser-internal';
@@ -22,45 +21,44 @@ export interface ThemeServiceSetupDeps {
 
 /** @internal */
 export class ThemeService {
-  private theme$ = new ReplaySubject<CoreTheme>(1);
-  private stop$ = new Subject<void>();
-
+  private contract?: ThemeServiceSetup;
   private themeMetadata?: InjectedMetadataTheme;
   private stylesheets: HTMLLinkElement[] = [];
 
   public setup({ injectedMetadata }: ThemeServiceSetupDeps): ThemeServiceSetup {
-    const theme = injectedMetadata.getTheme();
-    this.themeMetadata = theme;
+    const themeMetadata = injectedMetadata.getTheme();
+    this.themeMetadata = themeMetadata;
 
-    if (theme.darkMode === 'system' && browsersSupportsSystemTheme()) {
-      const darkMode = systemThemeIsDark();
-      this.applyTheme(darkMode);
-      // onSystemThemeChange((mode) => this.applyTheme(mode));
+    let theme: CoreTheme;
+    if (themeMetadata.darkMode === 'system' && browsersSupportsSystemTheme()) {
+      theme = { darkMode: systemThemeIsDark() };
     } else {
-      const darkMode = theme.darkMode === 'system' ? false : theme.darkMode;
-      this.applyTheme(darkMode);
+      const darkMode = themeMetadata.darkMode === 'system' ? false : themeMetadata.darkMode;
+      theme = { darkMode };
     }
 
-    return {
-      theme$: this.theme$.pipe(takeUntil(this.stop$), shareReplay(1)),
+    this.applyTheme(theme);
+
+    this.contract = {
+      getTheme: () => theme,
+      theme$: of(theme),
     };
+
+    return this.contract;
   }
 
   public start(): ThemeServiceStart {
-    if (!this.themeMetadata) {
+    if (!this.contract) {
       throw new Error('setup must be called before start');
     }
 
-    return {
-      theme$: this.theme$.pipe(takeUntil(this.stop$), shareReplay(1)),
-    };
+    return this.contract;
   }
 
-  public stop() {
-    this.stop$.next();
-  }
+  public stop() {}
 
-  private applyTheme(darkMode: boolean) {
+  private applyTheme(theme: CoreTheme) {
+    const { darkMode } = theme;
     this.stylesheets.forEach((stylesheet) => {
       stylesheet.remove();
     });
@@ -75,7 +73,6 @@ export class ThemeService {
 
     _setDarkMode(darkMode);
     updateKbnThemeTag(darkMode);
-    this.theme$.next({ darkMode });
   }
 }