Login Screen: Fix css for login screen dark mode (#20922) (#20946)

* Fix css for login screen dark mode

* Removes the outer-layout wrapper, moving the flexbox to the host

Sets the fallback for `--umb-auth-backdrop` to `--uui-color-surface`

---------

Co-authored-by: Lan Nguyen Thuy <lnt@umbraco.dk>
Co-authored-by: leekelleher <leekelleher@gmail.com>

src/Umbraco.Web.UI.Client/src/apps/app/app-auth.controller.ts

@@ -134,7 +134,7 @@ export class UmbAppAuthController extends UmbControllerBase {
 				},
 				modal: {
 					key: authModalKey,
-					backdropBackground: 'var(--umb-auth-backdrop, rgb(244, 244, 244))',
+					backdropBackground: 'var(--umb-auth-backdrop, var(--uui-color-surface))',
 				},
 			})
 			.onSubmit()

src/Umbraco.Web.UI.Client/src/packages/core/auth/modals/umb-app-auth-modal.element.ts

@@ -169,7 +169,10 @@ export class UmbAppAuthModalElement extends UmbModalBaseElement<UmbModalAppAuthC
 		UmbTextStyles,
 		css`
 			:host {
-				display: block;
+				display: flex;
+				justify-content: center;
+				width: 100vw;
+
 				background: var(--uui-color-background, #f4f4f4);
 
 				--curves-color: var(--umb-login-curves-color, #f5c1bc);