diff --git a/web/package-lock.json b/web/package-lock.json
index 4fadaa4..6b9fac3 100644
--- a/web/package-lock.json
+++ b/web/package-lock.json
@@ -13,6 +13,7 @@
 				"blurhash": "^2.0.5",
 				"katex": "^0.16.11",
 				"leaflet": "^1.9.4",
+				"monaco-editor": "^0.52.0",
 				"react": "^19.0.0",
 				"react-blurhash": "^0.3.0",
 				"react-dom": "^19.0.0",
@@ -4301,6 +4302,12 @@
 				"url": "https://github.com/sponsors/ljharb"
 			}
 		},
+		"node_modules/monaco-editor": {
+			"version": "0.52.0",
+			"resolved": "https://registry.npmjs.org/monaco-editor/-/monaco-editor-0.52.0.tgz",
+			"integrity": "sha512-OeWhNpABLCeTqubfqLMXGsqf6OmPU6pHM85kF3dhy6kq5hnhuVS1p3VrEW/XhWHc71P2tHyS5JFySD8mgs1crw==",
+			"license": "MIT"
+		},
 		"node_modules/ms": {
 			"version": "2.1.3",
 			"resolved": "https://registry.npmjs.org/ms/-/ms-2.1.3.tgz",
diff --git a/web/package.json b/web/package.json
index fe2c631..2f2a78e 100644
--- a/web/package.json
+++ b/web/package.json
@@ -15,6 +15,7 @@
 		"blurhash": "^2.0.5",
 		"katex": "^0.16.11",
 		"leaflet": "^1.9.4",
+		"monaco-editor": "^0.52.0",
 		"react": "^19.0.0",
 		"react-blurhash": "^0.3.0",
 		"react-dom": "^19.0.0",
diff --git a/web/src/api/types/preferences/types.ts b/web/src/api/types/preferences/types.ts
index 1b0e0a0..50211a1 100644
--- a/web/src/api/types/preferences/types.ts
+++ b/web/src/api/types/preferences/types.ts
@@ -21,6 +21,21 @@ export enum PreferenceContext {
 	RoomDevice = "room_device",
 }
 
+export function preferenceContextToInt(context: PreferenceContext): number {
+	switch (context) {
+	case PreferenceContext.Config:
+		return 0
+	case PreferenceContext.Account:
+		return 1
+	case PreferenceContext.Device:
+		return 2
+	case PreferenceContext.RoomAccount:
+		return 3
+	case PreferenceContext.RoomDevice:
+		return 4
+	}
+}
+
 export const anyContext = [
 	PreferenceContext.RoomDevice,
 	PreferenceContext.RoomAccount,
diff --git a/web/src/ui/settings/SettingsView.css b/web/src/ui/settings/SettingsView.css
index 61ae52e..cc0e7e7 100644
--- a/web/src/ui/settings/SettingsView.css
+++ b/web/src/ui/settings/SettingsView.css
@@ -56,6 +56,12 @@ div.settings-view {
 			font-family: var(--monospace-font-stack);
 		}
 
+		> div.vscode-wrapper {
+			position: fixed;
+			inset: 0;
+			z-index: 10;
+		}
+
 		> div.buttons {
 			display: flex;
 			justify-content: right;
diff --git a/web/src/ui/settings/SettingsView.tsx b/web/src/ui/settings/SettingsView.tsx
index 0c1d3fe..657d1c9 100644
--- a/web/src/ui/settings/SettingsView.tsx
+++ b/web/src/ui/settings/SettingsView.tsx
@@ -13,9 +13,17 @@
 //
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
-import { use, useCallback, useState } from "react"
+import { lazy, use, useCallback, useRef, useState } from "react"
+import Client from "@/api/client.ts"
 import { RoomStateStore, usePreferences } from "@/api/statestore"
-import { Preference, PreferenceContext, PreferenceValueType, Preferences, preferences } from "@/api/types/preferences"
+import {
+	Preference,
+	PreferenceContext,
+	PreferenceValueType,
+	Preferences,
+	preferenceContextToInt,
+	preferences,
+} from "@/api/types/preferences"
 import useEvent from "@/util/useEvent.ts"
 import ClientContext from "../ClientContext.ts"
 import JSONView from "../util/JSONView.tsx"
@@ -155,9 +163,24 @@ interface SettingsViewProps {
 	room: RoomStateStore
 }
 
+function getActiveCSSContext(client: Client, room: RoomStateStore): PreferenceContext {
+	if (room.localPreferenceCache.custom_css !== undefined) {
+		return PreferenceContext.RoomDevice
+	} else if (room.serverPreferenceCache.custom_css !== undefined) {
+		return PreferenceContext.RoomAccount
+	} else if (client.store.localPreferenceCache.custom_css !== undefined) {
+		return PreferenceContext.Device
+	} else {
+		return PreferenceContext.Account
+	}
+}
+
+const Monaco = lazy(() => import("../util/monaco.tsx"))
+
 const CustomCSSInput = ({ setPref, room }: { setPref: SetPrefFunc, room: RoomStateStore }) => {
 	const client = use(ClientContext)!
-	const [context, setContext] = useState(PreferenceContext.Account)
+	const appliedContext = getActiveCSSContext(client, room)
+	const [context, setContext] = useState(appliedContext)
 	const getContextText = useCallback((context: PreferenceContext) => {
 		if (context === PreferenceContext.Account) {
 			return client.store.serverPreferenceCache.custom_css
@@ -180,12 +203,30 @@ const CustomCSSInput = ({ setPref, room }: { setPref: SetPrefFunc, room: RoomSta
 		setText(evt.target.value)
 	}, [])
 	const onSave = useEvent(() => {
-		setPref(context, "custom_css", text)
+		if (vscodeOpen) {
+			setText(vscodeContentRef.current)
+			setPref(context, "custom_css", vscodeContentRef.current)
+		} else {
+			setPref(context, "custom_css", text)
+		}
 	})
 	const onDelete = useEvent(() => {
 		setPref(context, "custom_css", undefined)
 		setText("")
 	})
+	const [vscodeOpen, setVSCodeOpen] = useState(false)
+	const vscodeContentRef = useRef("")
+	const vscodeInitialContentRef = useRef("")
+	const onClickVSCode = useEvent(() => {
+		vscodeContentRef.current = text
+		vscodeInitialContentRef.current = text
+		setVSCodeOpen(true)
+	})
+	const closeVSCode = useCallback(() => {
+		setVSCodeOpen(false)
+		setText(vscodeContentRef.current)
+		vscodeContentRef.current = ""
+	}, [])
 	return <div className="custom-css-input">
 		<div className="header">
 			<h3>Custom CSS</h3>
@@ -195,9 +236,21 @@ const CustomCSSInput = ({ setPref, room }: { setPref: SetPrefFunc, room: RoomSta
 				<option value={PreferenceContext.RoomAccount}>Room (account)</option>
 				<option value={PreferenceContext.RoomDevice}>Room (device)</option>
 			</select>
+			{preferenceContextToInt(context) < preferenceContextToInt(appliedContext) &&
+				<span className="warning">
+					&#x26a0;&#xfe0f; This context will not be applied, <code>{appliedContext}</code> has content
+				</span>}
 		</div>
-		<textarea value={text} onChange={onChangeText}/>
+		{vscodeOpen ? <div className="vscode-wrapper">
+			<Monaco
+				initData={vscodeInitialContentRef.current}
+				onClose={closeVSCode}
+				onSave={onSave}
+				contentRef={vscodeContentRef}
+			/>
+		</div> : <textarea value={text} onChange={onChangeText}/>}
 		<div className="buttons">
+			<button onClick={onClickVSCode}>Open in VS Code</button>
 			{origText !== undefined && <button className="delete" onClick={onDelete}>Delete</button>}
 			<button className="save primary-color-button" onClick={onSave} disabled={origText === text}>Save</button>
 		</div>
diff --git a/web/src/ui/util/monaco.tsx b/web/src/ui/util/monaco.tsx
new file mode 100644
index 0000000..784ae41
--- /dev/null
+++ b/web/src/ui/util/monaco.tsx
@@ -0,0 +1,72 @@
+// gomuks - A Matrix client written in Go.
+// Copyright (C) 2024 Tulir Asokan
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+import "monaco-editor/esm/vs/basic-languages/css/css.contribution.js"
+import "monaco-editor/esm/vs/editor/edcore.main.js"
+import * as monaco from "monaco-editor/esm/vs/editor/editor.api.js"
+import CSSWorker from "monaco-editor/esm/vs/language/css/css.worker.js?worker"
+import "monaco-editor/esm/vs/language/css/monaco.contribution.js"
+import { RefObject, memo, useLayoutEffect, useRef } from "react"
+
+window.MonacoEnvironment = {
+	getWorker: function() {
+		return new CSSWorker()
+	},
+}
+
+export interface MonacoProps {
+	initData: string
+	onClose: () => void
+	onSave: () => void
+	contentRef: RefObject<string>
+}
+
+const Monaco = ({ initData, onClose, onSave, contentRef }: MonacoProps) => {
+	const container = useRef<HTMLDivElement>(null)
+	const editor = useRef<monaco.editor.IStandaloneCodeEditor>(null)
+	useLayoutEffect(() => {
+		if (!container.current) {
+			return
+		}
+		const newEditor = monaco.editor.create(container.current, {
+			language: "css",
+			value: initData,
+			fontLigatures: true,
+			fontFamily: `var(--monospace-font-stack)`,
+			theme: window.matchMedia("(prefers-color-scheme: dark)").matches ? "vs-dark" : "vs",
+		})
+		const model = newEditor.getModel()
+		if (!model) {
+			return
+		}
+		model.onDidChangeContent(() => contentRef.current = model.getValue(monaco.editor.EndOfLinePreference.LF))
+		newEditor.onKeyDown(evt => {
+			if (evt.keyCode === monaco.KeyCode.Escape) {
+				onClose()
+			} else if (evt.ctrlKey && evt.keyCode === monaco.KeyCode.KeyS) {
+				onSave()
+				evt.preventDefault()
+			}
+		})
+		newEditor.focus()
+		editor.current = newEditor
+		return () => newEditor.dispose()
+		// All props are intentionally immutable
+		// eslint-disable-next-line react-hooks/exhaustive-deps
+	}, [])
+	return <div style={{ width: "100%", height: "100%" }} ref={container}/>
+}
+
+export default memo(Monaco)
diff --git a/web/vite.config.ts b/web/vite.config.ts
index 0a18006..5d88b2d 100644
--- a/web/vite.config.ts
+++ b/web/vite.config.ts
@@ -2,16 +2,19 @@ import react from "@vitejs/plugin-react-swc"
 import { defineConfig } from "vite"
 import svgr from "vite-plugin-svgr"
 
+const splitDeps = ["katex", "leaflet", "monaco-editor"]
+
 export default defineConfig({
 	base: "./",
 	build: {
 		target: ["esnext", "firefox128", "chrome131", "safari18"],
+		chunkSizeWarningLimit: 3500,
 		rollupOptions: {
 			output: {
 				manualChunks: id => {
 					if (id.includes("wailsio")) {
 						return "wails"
-					} else if (id.includes("node_modules") && !id.includes("katex") && !id.includes("leaflet")) {
+					} else if (id.includes("node_modules") && !splitDeps.some(dep => id.includes(dep))) {
 						return "vendor"
 					} else if (id.endsWith("/emoji/data.json")) {
 						return "emoji"