Twenty Thirteen: Multisite register screen content is too wide

[kwight]

The Register screen for Multisite (wp-signup.php) is too wide; it has no defining widths for content.

With max-width 1040px

23631.diff​ adds a max-width of 1040px for .mu_register. Feel free to move it wherever seems appropriate.

Viewable in mu_signup_max_width.png​

I went a little heavier here with 23631.2.diff.

• Changed some markup in wp-signup.php, allowing better targeting of helper text (I don't believe it could affect anything in the wild)
• Removed some aggressive form field styling in wp-signup.php, which allows more consistent styling by inheritance (helps Twenty Twelve a bit too)
• Went with a narrower 604px single-column width for the form's container
• Some additional Twenty Thirteen specific styling

If there's interest in this direction, I'm assuming the signup.php changes should be done in a new separate ticket?..

Yes, please only patch Twenty Thirteen here. (The signup.php stuff in a different ticket.)

23631.3.diff styles Multisite forms without relying on wp-signup.php markup changes.

Good patch, Kirk -- only change I made was swap lines 2446 and 2447, for alphabetical properties within the block.

In 23513:

Twenty Thirteen: style the multisite registration form, props kwight. Fixes #23631.