Generally, the way to find the code of some feature is to open developer tools in the browser and activate the “select element” pointer (usually the most top left icon in developer tools).
Then point at the element that is operating the feature that you are interested in, and click.
This takes you to that element in the DOM browser in the developer tools.
Then look up the tree to find a meaningful class name, like
<div class="announcement">
Then search for that in the codebase. Usually class names are things like seek-graph-container or AnnouncementPreferences, which are easy to search for.
In the case of annoucement you’d probably need to search for className="announcement" (*) , so that the search is specific enough to find that it is instantiated here:
You can try using github’s search - type what you’re interested in the search bar. This is good for the first kind of element I mentioned, but hit-and-miss for more specific ones.
Rather easier/more reliable is to clone the repo and use your local tools to search.
(*): Noting that React converts className into class in the output because class is a js reserved word