There is no way to check if they have uploaded a file or not, (ie check to see if they have selected a valid upload file) unless this is done using some server-side language, after submission.
Self-Executing functions are just one good example that I'll try to demystify here.
The viewer will learn the benefit of using external CSS files and the relationship between class and ID selectors.
Create your external css file by saving it as style.css then set up your style tags:
Reference the nav tag and set your prop…