Adds additional type size steps

Adds intermediate font size steps between baseline and medium and
baseline and small. Updates mixins and variables accordingly.
Fixes error in functions

Color functions weren’t shading and tinting properly when opacity was
added. This commit fixes that issue by adding the shade and tint to the
opacity method.
Adjusts styles

- Adjusts button styles to make rollover more subtle.
- Adjusts responsive styles to hide “I need” text on small screens, and
increase size of button “Search” text.