We recommend using element with the Font Awesome CSS classes for the style
class for the style of icon you want to use and the icon name class with the
fa- prefix for the icon you want to use.
what is fas fa in html
Font Awesome is designed to be used with inline elements, and we recommend
sticking with a consistent HTML element to reference them by in your project.
... 1) its name, prefixed with fa- (meaning “font awesome” naturally!) and
2) the style you want to use's corresponding prefix**.