Hi there,
it would require some CSS.
To begin:
1. Add a Container Block and give it an Additional CSS Class of: has-ribbon
2. Add your content to the Container including a Headline Block for the ribbon.
2.1 Set the Headline > Spacing to Inline Width and give it some padding and colors.
2.2 Give your headline block a class of is-ribbon
3. Add this CSS to position the ribbon over the corner of the container.
.gb-container.has-ribbon {
position: relative;
}
.gb-headline.is-ribbon {
position: absolute;
top: -10px;
left: -10px;
}