(core) Support dark mode in custom widgets

Test Plan: Manual.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D4036

test/client/lib/SafeBrowser.ts

@@ -180,7 +180,13 @@ describe('SafeBrowser', function() {
   };
   function createSafeBrowser(mainPath: string): {safeBrowser: SafeBrowser, pluginRpc: Rpc} {
     const pluginInstance = new PluginInstance(localPlugin, {});
-    const safeBrowser = new SafeBrowser(pluginInstance, clientScope, '', mainPath, {});
+    const safeBrowser = new SafeBrowser({
+      pluginInstance,
+      clientScope,
+      untrustedContentOrigin: '',
+      mainPath,
+      baseLogger: {},
+    });
     cleanup.push(() => safeBrowser.deactivate());
     pluginInstance.rpc.registerForwarder(mainPath, safeBrowser);
     return {safeBrowser, pluginRpc: pluginInstance.rpc};