SyntaxError: import declarations may only appear at top level of a module

I am trying to use a plugin called "Simplebar" found on GitHub, GitHub SimpleBar but after downloading the scripts and looking at the simple.js script, it looks like it has an error

At the top of the simplebar.js file there are some import lines of code:

import scrollbarWidth from 'scrollbarwidth'
import debounce from 'lodash.debounce'

import './simplebar.css'

If I look in my browser debugger I see an error: "SyntaxError: import declarations may only appear at top level of a module". Has anyone tried to us this plugin. Many thanks in advance for your time.