JSFiddle - React, Tailwind, and code Playground

CSS

.video{ position: absolute; left: 150px; top: 150px; width: 350px; height: 5000px; background-color: black}

JavaScript

//

var scrolltotop={
	//startline: Integer. Number of pixels from top of doc scrollbar is scrolled before showing control
	//scrollto: Keyword (Integer, or "Scroll_to_Element_ID"). How far to scroll document up when control is clicked on (0=top).
	setting: {startline:100, scrollto: 0, scrollduration:1000, fadeduration:[500, 100]},
	controlHTML: '<img src="up.png" style="width:48px; height:48px" />', //HTML for control, which is auto wrapped in DIV w/ ID="topcontrol"
	controlattrs: {offsetx:5, offsety:5}, //offset of control relative to right/ bottom of window corner
	anchorkeyword: '#top', //Enter href value of HTML anchors on the page that should also act as "Scroll Up" links

	state: {isvisible:false, shouldvisible:false},

	scrollup:function(){
		if (!this.cssfixedsupport) //if control is positioned using JavaScript
			this.$control.css({opacity:0}) //hide control immediately after clicking it
		var dest=isNaN(this.setting.scrollto)? this.setting.scrollto : parseInt(this.setting.scrollto)
		if (typeof dest=="string" && jQuery('#'+dest).length==1) //check element set by string exists
			dest=jQuery('#'+dest).offset().top
		else
			dest=0
		this.$body.animate({scrollTop: dest}, this.setting.scrollduration);
	},

	keepfixed:function(){
		var $window=jQuery(window)
		var controlx=$window.scrollLeft() + $window.width() - this.$control.width() - this.controlattrs.offsetx
		var controly=$window.scrollTop() + $window.height() - this.$control.height() - this.controlattrs.offsety
		this.$control.css({left:controlx+'px', top:controly+'px'})
	},

	togglecontrol:function(){
		var scrolltop=jQuery(window).scrollTop()
		if (!this.cssfixedsupport)
			this.keepfixed()
		this.state.shouldvisible=(scrolltop>=this.setting.startline)? true : false
		if (this.state.shouldvisible && !this.state.isvisible){
			this.$control.stop().animate({opacity:1}, this.setting.fadeduration[0])
			this.state.isvisible=true
		}
		else if (this.state.shouldvisible==false &&...