fix button color changing on click and default message for input field

Addresses https://github.com/optimizely/marketing-website/issues/583

-fixed default test remaining in input on on screen in button when the user erases all the text
-changed z-indexing to allow for blue button to be clicked

To test, change the input field for button text, then erase it completely.  The default "boot it now" message should appear.  Click on various areas of the blue button to ensure that it works and changes button color on image.