Added consistent colors in display formats

assets/js/accordion.js

assets/js/countdown.js

assets/js/event-grid.js

assets/js/featured-banner.js

assets/js/teaser-list.js

cern_display_formats.libraries.yml

cern_display_formats.links.menu.yml

cern_display_formats.module

cern_display_formats.routing.yml

src/Form/DisplayFormatsSettingsForm.php

src/Plugin/views/style/Accordion.php

src/Plugin/views/style/TeaserList.php

src/Plugin/views/style/VerticalBoxes.php