Improve accessibility of focus state

[arinchoi03]

1. add $color-gold to be our new focus outline color (and add offset) for: a. text input b. textarea c. buttons d. radio buttons e. checkboxes f. select
   g. reveal h. link (WITHOUT OFFSET)
2. accordion: currently tabbing into them create a blue focus outline around the text. Will need some workaround
3. linked images are tabbable because they're inherently a elements (links). We need offset for linked images only. I see examples of linked images on the homepage that have the illustration class, so I'll be adding the offset there. For illustrations that do not get focus, this css change will have no impact.

• [x] code reviewed
• [x] design reviewed