Custom styles
Custom feedback styles apply custom colors, borders, focus styles, and background icons to better communicate feedback. Background icons for <select>s are only available with .custom-select, and not .form-control.
Tooltips
If your form layout allows it, you can swap the .{valid|invalid}-feedback classes for .{valid|invalid}-tooltip classes to display validation feedback in a styled tooltip. Be sure to have a parent with position: relative on it for tooltip positioning. In the example below, our column classes have this already, but your project may require an alternative setup.