gitlab-org--gitlab-foss/app/assets/stylesheets/sections/errors.scss

.error-page {
  max-width: 400px;
  margin: 0 auto;

  h1, h2, h3 {
    text-align: center;
  }

  h1 {
    font-size: 56px;
    line-height: 100px;
    font-weight: 300;
  }
}