The markdown-notices plugin for Grav allows generation of notice blocks of text via markdown:

This plugin is easy to install with GPM.

$ bin/gpm install markdown-notices

Simply copy the user/plugins/markdown-notices/markdown-notices.yaml into user/config/plugins/markdown-notices.yaml and make your modifications.

enabled: true
built_in_css: true
base_classes: 'notices'
level_classes: [yellow, red, blue, green]

Using one level of !

! Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris feugiat quam erat, ut iaculis diam posuere nec.
! Vestibulum eu condimentum urna. Vestibulum feugiat odio ut sodales porta. Donec sit amet ante mi. Donec lobortis
! orci dolor. Donec tristique volutpat ultricies. Nullam tempus, enim sit amet fringilla facilisis, ipsum ex
! tincidunt ipsum, vel placerat sem sem vitae risus. Aenean posuere sed purus nec pretium.

You will output the following HTML

<div class="notices yellow">
    <p>
        Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris feugiat quam erat, ut iaculis diam posuere nec.
        Vestibulum eu condimentum urna. Vestibulum feugiat odio ut sodales porta. Donec sit amet ante mi. Donec lobortis
        orci dolor. Donec tristique volutpat ultricies. Nullam tempus, enim sit amet fringilla facilisis, ipsum ex
        tincidunt ipsum, vel placerat sem sem vitae risus. Aenean posuere sed purus nec pretium.
    </p>
</div>

The notices class determined by the base_classes and yellow class is determined by the level_classes in the configuration. You can customize this as you need.

!! Lorem ipsum dolor sit amet, **consectetur adipiscing** elit. Mauris feugiat quam erat, ut iaculis diam posuere nec.
!!
!! * List item a
!! * List item b
!!
!! orci dolor. Donec tristique volutpat ultricies. Nullam tempus, enim sit amet fringilla facilisis, ipsum ex
!! tincidunt ipsum, vel placerat sem sem vitae risus. Aenean posuere sed purus nec pretium.

Two levels of !! will use the second level class etc. You can also use complex markdown inside the notices.