Fix <input> alignment

It turns out I had a non-standard monospace font set as my
default (Monoco instead of Courier), so the alignment of the input box
was slightly off on out-of-the-box Firefoxen.
Copy change: remove "CSS"

Got some feedback saying that "CSS" will probably be an impenetrable
acronym for new users so we are saying "code" instead.
Improve textbox style

From the feedback: it wasn't totally clear that the color input was
editable because it didn't look like an input. This attempts to address
those changes by adding a border and a light background to distinguish
it on the page.
New interaction

- Slow down the flyout
- Slow down the typing
- Select the input text after ghost writing
- Don't show the CTA until the user changes the bgcolor
New build