Fix/add focus styling

[troxler]

Hi. I maintain a list of CSS frameworks and there is a PR to add DoodleCSS.

While checking out your project, I noticed that the focus styling is a little lacking on some elements.

• Text inputs have an additional border around the doodle border. It might make sense to think about combining them into a single border. The doodle border could be blue, for example.

• Some elements like radio buttons and checkboxes do not have a focus styling at all.

Also note that empty paragraphs (e.g. within the fieldset) are not a good way to add vertical spacing.

[chr15m]

@troxler thank you for reporting these issues. I hope to fix them soon and I will let you know if/when that happens.