Add Container element

[Noxsios]

ex: https://github.com/defenseunicorns/zarf/blob/razzle-web-based-ui/src/ui/lib/components/container.svelte

A flexible container element for centering text content.

React equivalent: https://mui.com/material-ui/react-container/#main-content

[Noxsios]

something like:

<Box element="div" class="container">
    <slot />
</Box>

<style>
    .container {
        margin-left: auto;
        margin-right: auto;
        margin-bottom: 3rem;
    }
    @media (min-width: 768px) {
        .container {
            max-width: 56rem;
        }
    }
    @media (min-width: 1200px) {
        .container {
            max-width: 66rem;
        }
    }
</style>