Sorry to say but html outputs from this plugin have the worst code quality I've ever seen. Everything have same class, no way to select specific element to apply custom css. If they want to apply 10px height, they have a class for that. Background white, another class for that and bla bla bla.
This is the way this plugin shows button:
<a style="border:2px solid #78635a; color:#78635a;" href=".." class="nd_booking_padding_15_30_important nd_options_second_font_important nd_booking_border_radius_0_important nd_booking_background_color_transparent_important nd_booking_cursor_pointer nd_booking_display_inline_block nd_booking_font_size_11 nd_booking_font_weight_bold nd_booking_letter_spacing_2" target="_self">BOOK NOW FROM 25 $</a>
Every element have same classes but not a single unique class to identify what the element is. This makes it impossible to customize elements