During the 401 ASP.NET course, we will be learning a great deal of C# and the .NET Core Framework, But we will also be making use of technologies related to web development that are not C#. A solid working knowledge of HTML/CSS/JS is important for any web developer.
Spend the time between now and the start of class sharpening your HTML/CSS/JS skills.
Another great resource for all of the above is FreeCodeCamp . Once you sign up for an account there, you should be able to work your way all the way through the Advanced Algorithm Scripting section of work. It does take time though, so pace yourself over several days/weeks.