The following is a rough UI design for the Retro Board, which will be designed using Spring Thymeleaf for the web application:

The UI will consist of three columns for each particular comment type and a text area for typing comments. In the end, there will be a button to submit all comments. The UI has an additional requirement where it needs to refresh every 30 seconds to see updated comments from others. This UI will be implemented in a responsive way so that it can be used in desktop devices as well as mobile devices. In order to achieve this, the following UI framework will be used:

• Bootstrap: This is a very famous framework for developing responsive UIs for devices with different screen sizes and resolutions
• Font Awesome: This is a collection of icons that are usually used in UIs

The preceding frameworks will be used to implement the aforementioned UI design with standard HTML, CSS, and a bit of JavaScript.