Default UI redesign (#7429)

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* Update default.sidebar.vue

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* Update sticky-sidebar.ts

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* Update messaging-room.form.vue

* Update timeline.vue

src/client/components/signup-dialog.vue

@@ -7,7 +7,7 @@
 >
 	<template #header>{{ $ts.signup }}</template>
 
-	<div class="_section">
+	<div class="_root">
 		<XSignup :auto-set="autoSet" @signup="onSignup"/>
 	</div>
 </XModalWindow>