I would like this email field to be vertically centered with respect to the other elements in the form.

Hi - I have tried everything I can think of to get the email field vertically centered with the other fields in this form.  Can you tell me how to accomplish this?  Also, suddenly, a white line appeared above the header when I added the mobile responsive widget.  Any clue how to get rid of this as well?

Try to inject this CSS codes to your form, this should center the 3 elements under the header and remove the whitelist.

li#id_6 {

    width: 34%;

}

li#id_3 {

    width: 10%;

}

label#label_6 {

    display: none;

}

div#cid_6 {

    line-height: 69px;

}

iframe#customFieldFrame_6 {

    width: 100% !important;

}

button#input_3 {

    margin-top: 8px;

}

Guide: http://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes

Result:

If something went wrong, please let us know so we can further assist you here.

You might also want to clone these themes, they have horizontal fields design.

https://www.jotform.com/theme-store/theme/horizontal-flat

https://www.jotform.com/theme-store/theme/magnificient