Polish error page styling (#50916)
Polish default client error page styling:
* shrink the `line-height` to `2em` for better mobile display
* remove `text-align: left` to let the text center properly
#### After vs Before
(both **app router** and **pages** default client error page)
<p>
<img width="300" alt="image" src="https://github.com/vercel/next.js/assets/4800338/de7260af-7046-4783-8f82-8ac5f39f25b7">
<img width="300" alt="image" src="https://github.com/vercel/next.js/assets/4800338/f4207809-f11f-448d-95ec-0a32b54f3562">
</p>
#### After
(both **app router** and **pages** default client error page)
Closes NEXT-1263
