diff --git a/site/content/docs/03-run-time.md b/site/content/docs/03-run-time.md
index 386c18d5fd75..d07586ce4b76 100644
--- a/site/content/docs/03-run-time.md
+++ b/site/content/docs/03-run-time.md
@@ -906,6 +906,7 @@ The following initialisation options can be provided:
 | `props` | `{}` | An object of properties to supply to the component
 | `hydrate` | `false` | See below
 | `intro` | `false` | If `true`, will play transitions on initial render, rather than waiting for subsequent state changes
+| `customStyleTag` | `document.head` | An `HTMLElement` the styles should be appended to. It will only work if the component was compiled with the [`css: true` option](docs#svelte_compile).
 
 Existing children of `target` are left where they are.
 
diff --git a/src/compiler/compile/render_dom/index.ts b/src/compiler/compile/render_dom/index.ts
index fe1ee368fcd8..e204858df4f5 100644
--- a/src/compiler/compile/render_dom/index.ts
+++ b/src/compiler/compile/render_dom/index.ts
@@ -49,11 +49,8 @@ export default function dom(
 
 	if (should_add_css) {
 		body.push(b`
-			function ${add_css}() {
-				var style = @element("style");
-				style.id = "${component.stylesheet.id}-style";
-				style.textContent = "${styles}";
-				@append(@_document.head, style);
+			function ${add_css}(options) {
+				@append_styles(options, "${component.stylesheet.id.replace('svelte-', '')}", "${styles}");
 			}
 		`);
 	}
@@ -536,8 +533,10 @@ export default function dom(
 			class ${name} extends ${superclass} {
 				constructor(options) {
 					super(${options.dev && 'options'});
-					${should_add_css && b`if (!@_document.getElementById("${component.stylesheet.id}-style")) ${add_css}();`}
-					@init(this, options, ${definition}, ${has_create_fragment ? 'create_fragment': 'null'}, ${not_equal}, ${prop_indexes}, ${dirty});
+
+					${should_add_css && b`${add_css}(options);`}
+
+					@init(this, options, ${definition}, ${has_create_fragment ? 'create_fragment' : 'null'}, ${not_equal}, ${prop_indexes}, ${dirty});
 					${options.dev && b`@dispatch_dev("SvelteRegisterComponent", { component: this, tagName: "${name.name}", options, id: create_fragment.name });`}
 
 					${dev_props_check}
diff --git a/src/runtime/internal/Component.ts b/src/runtime/internal/Component.ts
index c503a507ffd2..73448c13133c 100644
--- a/src/runtime/internal/Component.ts
+++ b/src/runtime/internal/Component.ts
@@ -34,6 +34,7 @@ interface T$$ {
 	on_mount: any[];
 	on_destroy: any[];
 	skip_bound: boolean;
+	customStyleTag?: HTMLElement;
 }
 
 export function bind(component, name, callback) {
diff --git a/src/runtime/internal/dev.ts b/src/runtime/internal/dev.ts
index 74bf581bab51..41a78528c560 100644
--- a/src/runtime/internal/dev.ts
+++ b/src/runtime/internal/dev.ts
@@ -117,7 +117,8 @@ export class SvelteComponentDev extends SvelteComponent {
 	$$prop_def: Props;
 
 	constructor(options: {
-		target: Element;
+		target: Element | ShadowRoot;
+		customStyleTag: Element | ShadowRoot;
 		anchor?: Element;
 		props?: Props;
 		hydrate?: boolean;
@@ -216,7 +217,8 @@ export class SvelteComponentTyped<
 	$$slot_def: Slots;
 
 	constructor(options: {
-		target: Element;
+		target: Element | ShadowRoot;
+		customStyleTag: Element | ShadowRoot;
 		anchor?: Element;
 		props?: Props;
 		hydrate?: boolean;
diff --git a/src/runtime/internal/dom.ts b/src/runtime/internal/dom.ts
index 91e575ebf630..69cd8ed5e479 100644
--- a/src/runtime/internal/dom.ts
+++ b/src/runtime/internal/dom.ts
@@ -1,5 +1,27 @@
 import { has_prop } from './utils';
 
+let appendStylesTo = document.head;
+
+export function append_styles(
+	{ customStyleTag },
+	styleSheetId: string,
+	styles: string,
+	styleId:string = `svelte-${styleSheetId}-style`) {
+
+	if (customStyleTag) appendStylesTo = customStyleTag;
+
+	if (!appendStylesTo.querySelector('#' + styleId)) {
+		const style = element('style');
+		style.id = styleId;
+		style.textContent = styles;
+		append(appendStylesTo, style);
+	}
+}
+
+export function append_empty_stylesheet() {
+	return appendStylesTo.appendChild(element('style') as HTMLStyleElement);
+}
+
 export function append(target: Node, node: Node) {
 	target.appendChild(node);
 }
diff --git a/src/runtime/internal/style_manager.ts b/src/runtime/internal/style_manager.ts
index 8060e65a5d3f..4e16bdb3cf78 100644
--- a/src/runtime/internal/style_manager.ts
+++ b/src/runtime/internal/style_manager.ts
@@ -1,4 +1,4 @@
-import { element } from './dom';
+import { append_empty_stylesheet } from './dom';
 import { raf } from './environment';
 
 interface ExtendedDoc extends Document {
@@ -31,7 +31,7 @@ export function create_rule(node: Element & ElementCSSInlineStyle, a: number, b:
 	const name = `__svelte_${hash(rule)}_${uid}`;
 	const doc = node.ownerDocument as ExtendedDoc;
 	active_docs.add(doc);
-	const stylesheet = doc.__svelte_stylesheet || (doc.__svelte_stylesheet = doc.head.appendChild(element('style') as HTMLStyleElement).sheet as CSSStyleSheet);
+	const stylesheet = doc.__svelte_stylesheet || (doc.__svelte_stylesheet = append_empty_stylesheet().sheet as CSSStyleSheet);
 	const current_rules = doc.__svelte_rules || (doc.__svelte_rules = {});
 
 	if (!current_rules[name]) {
diff --git a/test/js/samples/collapses-text-around-comments/expected.js b/test/js/samples/collapses-text-around-comments/expected.js
index 67335ce2469e..e3e000094ff7 100644
--- a/test/js/samples/collapses-text-around-comments/expected.js
+++ b/test/js/samples/collapses-text-around-comments/expected.js
@@ -2,6 +2,7 @@
 import {
 	SvelteComponent,
 	append,
+	append_styles,
 	attr,
 	detach,
 	element,
@@ -13,11 +14,8 @@ import {
 	text
 } from "svelte/internal";
 
-function add_css() {
-	var style = element("style");
-	style.id = "svelte-1a7i8ec-style";
-	style.textContent = "p.svelte-1a7i8ec{color:red}";
-	append(document.head, style);
+function add_css(options) {
+	append_styles(options, "1a7i8ec", "p.svelte-1a7i8ec{color:red}");
 }
 
 function create_fragment(ctx) {
@@ -58,7 +56,7 @@ function instance($$self, $$props, $$invalidate) {
 class Component extends SvelteComponent {
 	constructor(options) {
 		super();
-		if (!document.getElementById("svelte-1a7i8ec-style")) add_css();
+		add_css(options);
 		init(this, options, instance, create_fragment, safe_not_equal, { foo: 0 });
 	}
 }
diff --git a/test/js/samples/css-media-query/expected.js b/test/js/samples/css-media-query/expected.js
index f4776700599d..749c692aa143 100644
--- a/test/js/samples/css-media-query/expected.js
+++ b/test/js/samples/css-media-query/expected.js
@@ -1,7 +1,7 @@
 /* generated by Svelte vX.Y.Z */
 import {
 	SvelteComponent,
-	append,
+	append_styles,
 	attr,
 	detach,
 	element,
@@ -11,11 +11,8 @@ import {
 	safe_not_equal
 } from "svelte/internal";
 
-function add_css() {
-	var style = element("style");
-	style.id = "svelte-1slhpfn-style";
-	style.textContent = "@media(min-width: 1px){div.svelte-1slhpfn{color:red}}";
-	append(document.head, style);
+function add_css(options) {
+	append_styles(options, "1slhpfn", "@media(min-width: 1px){div.svelte-1slhpfn{color:red}}");
 }
 
 function create_fragment(ctx) {
@@ -41,7 +38,7 @@ function create_fragment(ctx) {
 class Component extends SvelteComponent {
 	constructor(options) {
 		super();
-		if (!document.getElementById("svelte-1slhpfn-style")) add_css();
+		add_css(options);
 		init(this, options, null, create_fragment, safe_not_equal, {});
 	}
 }
diff --git a/test/sourcemaps/samples/compile-option-dev/test.js b/test/sourcemaps/samples/compile-option-dev/test.js
index bf240a5a8927..750a6afc640d 100644
--- a/test/sourcemaps/samples/compile-option-dev/test.js
+++ b/test/sourcemaps/samples/compile-option-dev/test.js
@@ -4,8 +4,8 @@ const b64dec = s => Buffer.from(s, 'base64').toString();
 
 export async function test({ assert, css,  js }) {
 
-    // We check that the css source map embedded in the js is accurate
-    const match = js.code.match(/\tstyle\.textContent = "(.*?)(?:\\n\/\*# sourceMappingURL=data:(.*?);charset=(.*?);base64,(.*?) \*\/)?";\n/);
+	// We check that the css source map embedded in the js is accurate
+	const match = js.code.match(/\tappend_styles\(options, ".{6}", "(.*?)(?:\\n\/\*# sourceMappingURL=data:(.*?);charset=(.*?);base64,(.*?) \*\/)?"\);\n/);
 	assert.notEqual(match, null);
 
 	const [mimeType, encoding, cssMapBase64] = match.slice(2);