wagtail/client/scss/components/_messages.scss

// Messages are specific to Django's 'Messaging' system which adds messages into the session,
// for display on the next page visited. These appear as an animated banner at the top of the page.
// For inline help text, see typography.scss
.messages {
  position: relative;
  background-color: theme('colors.surface-page');

  .buttons {
    margin-inline-start: 1em;
  }

  > ul {
    @include unlistimmediate();
    position: relative;
    top: -100px;
    opacity: 0;
  }

  > ul > li {
    padding: 1.6em 3em 1.6em 1.6em;
    color: theme('colors.text-button');
    border-bottom: 1px solid transparent;
  }

  > ul > li:before {
    @include font-smoothing;
    margin-inline-end: 0.5em;
    font-size: 1.5em;
    vertical-align: middle;
  }

  &-icon {
    vertical-align: text-top;
    margin-inline-end: 0.5em;
    width: 1.5em;
    height: 1.5em;
  }

  .button.button-secondary {
    border-color: currentColor;
    color: inherit;

    &:hover {
      background-color: transparent;
      color: theme('colors.text-button');
    }
  }

  .error {
    background-color: theme('colors.critical.200');
    color: theme('colors.white.DEFAULT');

    .button:hover {
      color: theme('colors.white.DEFAULT');
    }
  }

  .warning {
    background-color: theme('colors.warning.100');
    color: theme('colors.grey.600');

    @include more-contrast() {
      background-color: theme('colors.warning.75');
    }
  }

  .info {
    background-color: theme('colors.info.100');
    color: theme('colors.white.DEFAULT');
  }

  .success {
    background-color: theme('colors.positive.100');
    color: theme('colors.white.DEFAULT');
  }

  .errorlist {
    margin: 0.5em 0 0 1em;
  }
}

.messages.new > ul {
  transition: none;
  top: -100px;
}

.ready .messages > ul,
.messages.appear > ul {
  transition:
    top 0.5s ease,
    opacity 0.5s ease,
    max-height 1.2s ease;
  opacity: 1;
  top: 0;
}

@include media-breakpoint-up(sm) {
  .messages > ul > li {
    padding-inline-start: 1.6em;
    padding-inline-end: 3em;
  }
}