wagtail/wagtail/admin/static_src/wagtailadmin/scss/layouts/404.scss

@import '../../../../../../client/scss/settings';
@import '../../../../../../client/scss/tools';

.page404__bg {
  position: fixed;
  top: 0;
  // Remove once we drop support for Safari 13.
  // stylelint-disable-next-line property-disallowed-list
  left: 0;
  inset-inline-start: 0;
  width: 100vw;
  height: 100vh;
  background-color: $color-teal-darker;
  font-family: $font-sans;
  color: $color-white;
}

.page404__wrapper {
  position: absolute;
  top: 50%;
  // Remove once we drop support for Safari 13.
  // stylelint-disable-next-line property-disallowed-list
  left: 50%;
  inset-inline-start: 50%;
  transform: translate(-50%, -50%);
  display: flex;
  justify-content: center;
  align-items: center;
}

.wagtail-logo-container__desktop {
  float: left;
  width: 400px;
  height: 500px;
}

.page404__text-container {
  float: right;
  width: 600px;
  height: 500px;
  text-align: center;
}

.page404__header {
  font-size: 6.8em;
  margin-bottom: 0.2em;
  color: inherit;
}

.page404__text {
  font-size: 2.25em;
  line-height: 1.25em;
  color: inherit;
}

a.button.page404__button {
  // more specific to override standard button styles
  font-size: 1.5em;
  line-height: 2em;
  height: 2.5em;
  padding: 0 0.5em;
  background-color: $color-teal-darker;
  border: 4px solid $color-teal;
  color: inherit;

  &:hover {
    background-color: $color-teal;
  }
}

// SMALL DESKTOP CHANGES:
@include media-breakpoint-down(sm) {
  .wagtail-logo-container__desktop {
    display: none;
  }
}

// MOBILE CHANGES:
@include media-breakpoint-down(xs) {
  .page404__text-container {
    width: 400px;
  }

  .page404__header {
    font-size: 5em;
  }
}