Coming back to this, I will mark this as solved because it does a great job of targeting almost all (but not accordions) borders and essentially making them invisible across the entire form.
.fd-form .k-autocomplete, .fd-form .k-dateinput-wrap, .fd-form .k-dropdown-wrap, .fd-form .k-picker-wrap, .fd-form .k-multiselect-wrap, .fd-form .k-numeric-wrap, .fd-form .k-editor, .fd-form .k-upload, .fd-form .form-control.k-widget:not(.k-autocomplete), .fd-form .form-control{
border-width: 0px!important;
border: 0!important;
}
For those who want to target specific fields v. the near-global result above, try adding this CSS:
/* ////>>>>>>>>>>>>>> Only defined fields have borders invisible */
/* Only affect fields whose container has .custom-no-border */
.fd-form .custom-no-border .k-autocomplete,
.fd-form .custom-no-border .k-dateinput-wrap,
.fd-form .custom-no-border .k-dropdown-wrap,
.fd-form .custom-no-border .k-picker-wrap,
.fd-form .custom-no-border .k-multiselect-wrap,
.fd-form .custom-no-border .k-numeric-wrap,
.fd-form .custom-no-border .k-editor,
.fd-form .custom-no-border .k-upload,
.fd-form .custom-no-border .form-control.k-widget:not(.k-autocomplete),
.fd-form .custom-no-border .form-control,
.fd-form .custom-no-border .k-input,
.fd-form .custom-no-border .k-input-inner {
border: 0 !important;
box-shadow: none !important; /* kills focus/hover outlines in modern themes */
}
/* Make sure hover/focus doesn’t bring borders back */
.fd-form .custom-no-border .k-autocomplete:hover,
.fd-form .custom-no-border .k-dateinput-wrap:hover,
.fd-form .custom-no-border .k-dropdown-wrap:hover,
.fd-form .custom-no-border .k-picker-wrap:hover,
.fd-form .custom-no-border .k-multiselect-wrap:hover,
.fd-form .custom-no-border .k-numeric-wrap:hover,
.fd-form .custom-no-border .form-control:hover,
.fd-form .custom-no-border .k-autocomplete.k-focus,
.fd-form .custom-no-border .k-dateinput-wrap.k-focus,
.fd-form .custom-no-border .k-dropdown-wrap.k-focus,
.fd-form .custom-no-border .k-picker-wrap.k-focus,
.fd-form .custom-no-border .k-multiselect-wrap.k-focus,
.fd-form .custom-no-border .k-numeric-wrap.k-focus,
.fd-form .custom-no-border .form-control:focus {
border: 0 !important;
box-shadow: none !important;
}
/* If your Kendo theme exposes CSS vars for borders, zero those out locally */
.fd-form .custom-no-border {
--kendo-component-border-width: 0;
--kendo-input-border-width: 0;
}
Then apply custom-no-border to the GENERAL Class, like so in Plumsail Designer: