From f9275b88c4caeae40752cc429a4a8c9c5697394c Mon Sep 17 00:00:00 2001
From: Daniel Kimmich <d.kimmich@onventis.de>
Date: Wed, 16 Jul 2025 10:40:28 +0200
Subject: [PATCH] feat: allow custom root selector

---
 .../src/lib/material-css-vars.service.spec.ts | 28 +++++++++++++++++++
 .../src/lib/material-css-vars.service.ts      | 19 ++++++++++++-
 projects/material-css-vars/src/lib/model.ts   |  6 ++++
 3 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/projects/material-css-vars/src/lib/material-css-vars.service.spec.ts b/projects/material-css-vars/src/lib/material-css-vars.service.spec.ts
index afe54f4..9af129d 100644
--- a/projects/material-css-vars/src/lib/material-css-vars.service.spec.ts
+++ b/projects/material-css-vars/src/lib/material-css-vars.service.spec.ts
@@ -218,4 +218,32 @@ describe("MaterialCssVarsService", () => {
       );
     });
   });
+
+  describe("_getRootElement", () => {
+    it("should return the html if no root selector is set", () => {
+      const rootElement = service["_getRootElement"](undefined);
+
+      expect(rootElement).toBe(document.documentElement);
+    });
+
+    it("should return the element matching the root selector", () => {
+      const mockElement = document.createElement("app-root");
+      const spy = spyOn(document, "querySelector").and.returnValue(mockElement);
+
+      const rootElement = service["_getRootElement"]("app-root");
+
+      expect(rootElement).toBe(mockElement);
+      expect(spy).toHaveBeenCalledWith("app-root");
+    });
+
+    it("should warn and fall back to the html element if the passed root selector cannot be found", () => {
+      spyOn(console, "warn");
+      spyOn(document, "querySelector").and.returnValue(null);
+
+      const rootElement = service["_getRootElement"]("non-existing");
+
+      expect(rootElement).toBe(document.documentElement);
+      expect(console.warn).toHaveBeenCalledTimes(1);
+    });
+  });
 });
diff --git a/projects/material-css-vars/src/lib/material-css-vars.service.ts b/projects/material-css-vars/src/lib/material-css-vars.service.ts
index ff95af1..9970d4d 100644
--- a/projects/material-css-vars/src/lib/material-css-vars.service.ts
+++ b/projects/material-css-vars/src/lib/material-css-vars.service.ts
@@ -5,6 +5,7 @@ import {
   RendererFactory2,
   RendererStyleFlags2,
   DOCUMENT,
+  isDevMode,
 } from "@angular/core";
 import { Numberify, RGBA, TinyColor } from "@ctrl/tinycolor";
 import {
@@ -58,7 +59,7 @@ export class MaterialCssVarsService {
     @Inject(MATERIAL_CSS_VARS_CFG) cfg: MaterialCssVariablesConfig,
   ) {
     this.renderer = rendererFactory.createRenderer(null, null);
-    this.ROOT = this.document.documentElement;
+    this.ROOT = this._getRootElement(cfg.rootSelector);
 
     this.cfg = {
       ...DEFAULT_MAT_CSS_CFG,
@@ -433,4 +434,20 @@ export class MaterialCssVarsService {
     const darkest = Math.min(luminance1, luminance2);
     return (brightest + 0.05) / (darkest + 0.05);
   }
+
+  private _getRootElement(rootSelector: string | undefined): HTMLElement {
+    if (typeof rootSelector !== "string") {
+      return this.document.documentElement;
+    }
+    const rootElement = document.querySelector<HTMLElement>(rootSelector);
+    if (rootElement) {
+      return rootElement;
+    }
+    if (isDevMode()) {
+      console.warn(
+        `[MaterialCssVars] Could not find root element: ${rootSelector}. Falling back to HTML element.`,
+      );
+    }
+    return this.document.documentElement;
+  }
 }
diff --git a/projects/material-css-vars/src/lib/model.ts b/projects/material-css-vars/src/lib/model.ts
index 3192383..be38714 100644
--- a/projects/material-css-vars/src/lib/model.ts
+++ b/projects/material-css-vars/src/lib/model.ts
@@ -54,6 +54,12 @@ export interface MaterialCssVariablesConfig {
   darkThemeClass: string;
   lightThemeClass: string;
 
+  /**
+   * Selector to which the CSS variables are added.
+   * If not specified, the document's HTML element is used.
+   */
+  rootSelector?: string;
+
   colorMap: MaterialCssColorMapperEntry[];
   sortedHues: HueValue[];