diff --git a/addons/addon-fit/src/FitAddon.ts b/addons/addon-fit/src/FitAddon.ts
index a282ed3f8c..2cc8485789 100644
--- a/addons/addon-fit/src/FitAddon.ts
+++ b/addons/addon-fit/src/FitAddon.ts
@@ -23,6 +23,17 @@ interface ITerminalDimensions {
 const MINIMUM_COLS = 2;
 const MINIMUM_ROWS = 1;
 
+function getWindow(e: Node): Window {
+  if (e?.ownerDocument?.defaultView) {
+    return e.ownerDocument.defaultView.window;
+  }
+
+  return window;
+}
+function getComputedStyle(el: HTMLElement): CSSStyleDeclaration {
+  return getWindow(el).getComputedStyle(el, null);
+}
+
 export class FitAddon implements ITerminalAddon , IFitApi {
   private _terminal: Terminal | undefined;
 
@@ -69,10 +80,10 @@ export class FitAddon implements ITerminalAddon , IFitApi {
       ? 0
       : (this._terminal.options.overviewRuler?.width || ViewportConstants.DEFAULT_SCROLL_BAR_WIDTH));
 
-    const parentElementStyle = window.getComputedStyle(this._terminal.element.parentElement);
+    const parentElementStyle = getComputedStyle(this._terminal.element.parentElement);
     const parentElementHeight = parseInt(parentElementStyle.getPropertyValue('height'));
     const parentElementWidth = Math.max(0, parseInt(parentElementStyle.getPropertyValue('width')));
-    const elementStyle = window.getComputedStyle(this._terminal.element);
+    const elementStyle = getComputedStyle(this._terminal.element);
     const elementPadding = {
       top: parseInt(elementStyle.getPropertyValue('padding-top')),
       bottom: parseInt(elementStyle.getPropertyValue('padding-bottom')),
diff --git a/src/browser/input/Mouse.ts b/src/browser/input/Mouse.ts
index c40a7cc782..da7eca35c2 100644
--- a/src/browser/input/Mouse.ts
+++ b/src/browser/input/Mouse.ts
@@ -1,3 +1,5 @@
+import * as dom from 'vs/base/browser/dom';
+
 /**
  * Copyright (c) 2017 The xterm.js authors. All rights reserved.
  * @license MIT
@@ -5,7 +7,7 @@
 
 export function getCoordsRelativeToElement(window: Pick<Window, 'getComputedStyle'>, event: {clientX: number, clientY: number}, element: HTMLElement): [number, number] {
   const rect = element.getBoundingClientRect();
-  const elementStyle = window.getComputedStyle(element);
+  const elementStyle = dom.getComputedStyle(element);
   const leftPadding = parseInt(elementStyle.getPropertyValue('padding-left'));
   const topPadding = parseInt(elementStyle.getPropertyValue('padding-top'));
   return [