move document.head to addCssToComponent method

src/compiler/compile/render_dom/index.ts

@@ -44,8 +44,8 @@ export default function dom(
 
 	if (should_add_css) {
 		body.push(b`
-			function ${add_css}(customStyleTag) {
+			function ${add_css}(target) {
-				@appendStyleIfNotPresent(customStyleTag, "${component.stylesheet.id.replace('svelte-', '')}", "${styles}");
+				@appendStyleIfNotPresent(target, "${component.stylesheet.id.replace('svelte-', '')}", "${styles}");
 			}
 		`);
 	}

src/runtime/internal/Component.ts

@@ -102,7 +102,7 @@ export function addCssToComponent(component, add_css, options) {
 	component.$$ = {
 		customStyleTag: options.customStyleTag || current_component && current_component.$$.customStyleTag
 	};
-	add_css(component.$$.customStyleTag);
+	add_css(component.$$.customStyleTag || document.head);
 }
 
 export function init(component, options, instance, create_fragment, not_equal, props, dirty = [-1]) {

src/runtime/internal/dom.ts

@@ -1,7 +1,7 @@
 import { has_prop } from './utils';
 
 export function appendStyleIfNotPresent(
-	target: Element = document.head,
+	target: Element,
 	styleSheetId: string,
 	styles: string,
 	styleId:string = `svelte-${styleSheetId}-style`) {