[Bug report] Center elements on 404 pages

[onedonedone]

Description

In recent versions, the 404 messages are in the top left corner of the page, which are different from older versions.

Reproduction

https://stackblitz.com/edit/vuepress-cjc9nc?file=package.json

Used Package Manager

npm

System Info

System:
    OS: Linux 5.15 Ubuntu 22.04.3 LTS 22.04.3 LTS (Jammy Jellyfish)
    CPU: (6) x64 Intel(R) Core(TM) i5-8500 CPU @ 3.00GHz
    Memory: 5.12 GB / 7.73 GB
    Shell: 5.1.16 - /bin/bash
  Binaries:
    Node: 20.14.0 - ~/.nvm/versions/node/v20.14.0/bin/node
    Yarn: Not Found
    npm: 10.7.0 - ~/.nvm/versions/node/v20.14.0/bin/npm
    pnpm: Not Found
    bun: Not Found
  Utilities:
    Git: 2.34.1 - /usr/bin/git
  Browsers:
    Chrome: Not Found
  npmPackages:
    @vuepress/bundler-vite: 2.0.0-rc.14 => 2.0.0-rc.14 
    @vuepress/bundler-webpack: Not Found
    @vuepress/cli:  2.0.0-rc.14 
    @vuepress/client:  2.0.0-rc.14 
    @vuepress/core:  2.0.0-rc.14 
    @vuepress/markdown:  2.0.0-rc.14 
    @vuepress/shared:  2.0.0-rc.14 
    @vuepress/utils:  2.0.0-rc.14 
    vue: 3.4.29 => 3.4.29 
    vue-router:  4.4.0 
    vuepress: 2.0.0-rc.14 => 2.0.0-rc.14