/locomotivemtl/sass/helpers/_stack-context.scss

_objects.modal.scss

@import '_zindex.scss'

.modal {
	z-index: index($site-order, modals);

	.field {
		z-index: index($modal-order, fields);
	}

	.form-controls {
		z-index: index($modal-order, form-controls);
	}

	.error {
		z-index: index($modal-order, errors);
	}

	.autocomplete-dropdown {
		z-index: index($modal-order, autocomplete-dropdown);
	}

}

@import '_zindex.scss'

$modal-order: append($modal-order, close-button);
site-order: insert-nth($site-order, sidebar-filters, 3);

.modal .close-button {
   z-index: index($modal-order, close-button);
}

.sidebar-filter {
   z-index: index($site-order, sidebar-filter);
}   

_settings.z-index.scss

// Z-Index Master List

$site-order  : (project-covers: 1000, user-tooltip: 1030, sorting-bar: 1010, modals: 1040, navigation: 1020);
$modal-order : fields, form-controls, errors, autocomplete-dropdown;

output.css

.modal {
	z-index: 4;
}

.modal .field {
	z-index: 1;
}

.modal .form-controls {
	z-index: 2;
}

.modal .error {
	z-index: 3;
}

.modal .autocomplete-dropdown {
	z-index: 4;
}