If you don’t find it then add the following CSS code in the Custom CSS code option of your theme on the below path.

Admin Area -> Appearance -> Theme Settings -> Custom Code -> CSS Code

 

div#page-container #content .contact-form input,
div#page-container #content .contact-form textarea {
    border-width: 1px;
}

This code solves it partially. First of all, it also adds border to the submit button

so you need to add ( :not([type=submit]) )

........ .contact-form input:not([type=submit]),
div#page-container #content .contact-form textarea {
    border-width: 1px;
}

Moreover, it still doesn’t display labels above the input fields not using style 2 nor using styles 3,4,5.