Fix for :global(...) styles in custom elements. Close sveltejs#2969

Author: kmmbvnr

src/compiler/compile/render_dom/index.ts

@@ -442,7 +442,7 @@ export default function dom(
 				constructor(options) {
 					super();
 
-					${css.code && b`this.shadowRoot.innerHTML = \`<style>${css.code.replace(/\\/g, '\\\\')}${options.dev ? `\n/*# sourceMappingURL=${css.map.toUrl()} */` : ''}</style>\`;`}
+					${css.code && b`this.shadowRoot.innerHTML = \`<style>${css.code.replace(/\\/g, '\\\\').replace(/:global\(([-.\w]+)\)/g, '$1')}${options.dev ? `\n/*# sourceMappingURL=${css.map.toUrl()} */` : ''}</style>\`;`}
 
 					@init(this, { target: this.shadowRoot }, ${definition}, ${has_create_fragment ? 'create_fragment': 'null'}, ${not_equal}, ${prop_indexes}, ${dirty});
 

test/custom-elements/samples/global-styles/main.svelte

@@ -0,0 +1,9 @@
+<svelte:options tag="custom-element"/>
+
+<style>
+:global(p.active) {
+	color:rgb(128, 128, 128);
+}
+</style>
+
+<p></p>

test/custom-elements/samples/global-styles/test.js

@@ -0,0 +1,12 @@
+import * as assert from 'assert';
+import CustomElement from './main.svelte';
+
+export default function (target) {
+	new CustomElement({
+		target
+	});
+
+	const style = target.querySelector('custom-element').shadowRoot.querySelector('style');
+
+	assert.equal(style.textContent, 'p.active{color:rgb(128, 128, 128)}');
+}