This content comes from stacks
You can manage everything that comes in this "Jumbotron" in your stack. Think of forms, images, butons, headings, you name it. If you scroll a bit to the bottom, you will see an example outside a "container", filling the whole screen. Notice how the corners are automatically rounded in this one, and square in the other.
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You can use multiple stacks to add content to a "Jumbotron".