.NET developers are full stack developers who have a high level of proficiency in their specialised languages and tools (whether that's .NET core, AngularJS, Go or other languages), and are able to contribute to (or on some occasions take ownership of) a task, project or solution and its delivery. Whilst it may not be necessary to be an expert in front end languages, they would be expected to be able to adapt and pick up any new technologies required.
A good developer will be curious about all aspects of technology, and be an enthusiastic learner. They will enjoy challenges, and be open and transparent about the problems they face, and will enjoy helping colleagues resolve their own problems without judgement.