can not see the form fields on my website for contact page

There is a lot you can configure in forms, but what i can not seemt to find is how to show a border of a field in a form or to define the background. www.penart.be/contact

Editing the colours of the selected theme (applied to the form) doesn't help, i have put every possible colour to white.
it is impossible to display the the background of the form fields white or to show the borders of the fields.

attached a quick photoshop of what i'm looking for ...

Thanks for your help, have spend a lot of time to change setting, no succes,
squarespace support referred met to this solution which is not really what i'm looking for
https://share.squarespace.com/E0uejlre

thanks 
Bram

You can use this code to Website > Website Tools > Custom CSS.

div#block-665e1a70bda8054f3b514a14 input, div#block-665e1a70bda8054f3b514a14 textarea {
    background-color: #fff !important;
}

thank you for your help tuanphan!  🙂
works fine like this

meanwhile squarespace support escalated the problem to engineering to look into it, there seems to be something wrong with forms in general on my website; no modifications i do in the form visualisation is applied ... 

as it is the same block ID the button also show white without text, how can i add a css for this please?

I see it shows fine now