Add some minimal styling to make block visible in editor.

[martinDolan]

I noticed after creating a new block that at first it was nowhere to be found on the page. I think we should add some minimal styling to the block in the editor (outline, padding) to make it visible.

Suggestion:

In global.scss

.wp-block-post-content {
    @apply p-24;
    .wp-block {
        @apply p-4 outline outline-1 outline-primary-300;
    }
}

Before:

After

Here's a video screencast describing the problem: https://www.loom.com/share/23da3e5304044453a560a64d7dd164bc?sid=1bf04088-98dd-479d-8e2c-a0563f5997bd

[martinDolan]

See PR #21