JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html lang="es"><head></head>
    <style type="text/css">#calendar {
position: absolute;
top: 4px;
left: 530px;
width: 171px;
}
.wrapper {
background-color: #f5f5f5;
-webkit-border-bottom-right-radius: 10px;
-webkit-border-bottom-left-radius: 10px;
-moz-border-radius-bottomright: 10px;
-moz-border-radius-bottomleft: 10px;
border-bottom-right-radius: 10px;
border-bottom-left-radius: 10px;
padding: 2px;
margin-top:-1px;
}
        h3 {
background-color: #404040;
font-family: "Georgia", serif;
font-size: 8.5pt;
color: #fff;
border-bottom: 1px dotted #c5c5c5;
letter-spacing: 3pt;
padding-left: 2px;
margin: 0 0 5px;
text-transform: uppercase;
}
        strong {
background-color: #cad166;
color: #fff;
padding: 0 2px;
}
        
    </style>
  <body>
    
<div id="calendar">
<div class="wrapper"><h3><center>Calendar</center></h3>
<SCRIPT language="JavaScript">

monthnames = new Array(
"January",
"February",
"March",
"April",
"May",
"June",
"July",
"August",
"September",
"October",
"November",
"December");
var linkcount=0;
function addlink(month, day, href) {
var entry = new Array(3);
entry[0] = month;
entry[1] = day;
entry[2] = href;
this[linkcount++] = entry;
}
Array.prototype.addlink = addlink;
linkdays = new Array();
monthdays = new Array(12);
monthdays[0]=31;
monthdays[1]=28;
monthdays[2]=31;
monthdays[3]=30;
monthdays[4]=31;
monthdays[5]=30;
monthdays[6]=31;
monthdays[7]=31;
monthdays[8]=30;
monthdays[9]=31;
monthdays[10]=30;
monthdays[11]=31;
todayDate=new Date();
thisday=todayDate.getDay();
thismonth=todayDate.getMonth();
thisdate=todayDate.getDate();
thisyear=todayDate.getYear();
thisyear = thisyear % 100;
thisyear = ((thisyear < 50) ? (2000 + thisyear) : (1900 + thisyear));
if (((thisyear % 4 == 0) 
&& !(thisyear % 100 == 0))
||(thisyear % 400 == 0)) monthdays[1]++;
startspaces=thisdate;
while (startspaces > 7) startspaces-=7;
startspaces = thisday - startspaces + 1;
if...