Improve input padding, fix #18237.

## What does this MR do?
Improves horizontal padding for input fields.

## What are the relevant issue numbers?
#18237

## Screenshots (if relevant)

Before:

![Screen_Shot_2016-06-06_at_12.11.07_PM](/uploads/11d24c84e1ca8d268a5acc2b4e10bb77/Screen_Shot_2016-06-06_at_12.11.07_PM.png)

After:

![Screen_Shot_2016-06-06_at_12.10.38_PM](/uploads/cbb407d8fca1e8dc1ace2af6c0774181/Screen_Shot_2016-06-06_at_12.10.38_PM.png)

cc: @jschatz1 

See merge request !4489