feature(nestedinput): make button below input on less than 320px,eng-222

[wliederer]

adjusted button

above 320 px width

below 320px

[linear[bot]]

ENG-222 Break NestedInput in smaller breakpoints

As the container shrinks, the NestedInput component becomes more difficult to use. Below 320px, the nested input should "break" into its individual components — the input by itself, then the button centered on the next line. Make sure this occurs for all variations of the component, and write appropriate tests to accompany this function.