How can I change the current format of the text element on my form?

 - How could I get the 'Number in each age group' text field to not be in a box - just black on white?

This can be possible with the next CSS code: 

- This in case you need to clear up the format for all the text elements on your form: 

li[data-type="control_text"] .form-input-wide {

    background: transparent !important;

    border-width: 0px !important ;

}

- This in case you need to clear up the form for that specific text element: 

li#id_74 .form-input-wide {

    background: transparent !important;

    border-width: 0px !important ;

}

This guide will help you injecting the code to your form: https://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes 

I hope this helps.