`theme-apple-basic`, `intro`: title & subtitle isn't centered

[gy-mate]

Steps to reproduce

1. Run:

   npm init slidev@latest

2. Change the content of slides.md to this:

   ---
   theme: apple-basic
   layout: intro
   ---
   
   # Presentation title
   
   Presentation subtitle
   
   <div class="absolute bottom-10">
     <span class="font-700">
       Author and Date
     </span>
   </div>
   

Expected result

A correctly horizontally centered title and subtitle:

Actual result

A title and subtitle that isn't horizontally centered:

Relevant code

themes/packages/theme-apple-basic/layouts/intro.vue

Lines 1 to 7 in e87225c

	<template>
	<div class="slidev-layout intro">
	<div class="my-auto">
	<slot />
	</div>
	</div>
	</template>

cc @JeremyMeissner

[ISOR3X]

I have the same issue, but I am also curious as to why the background isn't black as shown in the preview images.