Angular.js - 在添加到待办事项列表中的项目上添加颜色/类

I'm having trouble adding a class to a form I have on my site. Basically what I'm trying to do is make an event list, where you input an event name, select from four options that categorize the event into categories 1, 2, 3 or 4. Depending on which category you select and click "Add Event", it should add a class to the text that is inputted and post it below in a list format, with that color added to the text. I cannot figure out how to add a class to what is added to the list. I'm pretty new to angular so any help would be appreciated.I'm having trouble adding a class to a form I h