JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://visjs.github.io/vis-timeline/standalone/umd/vis-timeline-graph2d.min.js"></script>
<link href="https://visjs.github.io/vis-timeline/styles/vis-timeline-graph2d.min.css" rel="stylesheet"/>

<div id="visualization"></div>

CSS

body,
html {
  font-family: sans-serif;
}

/* 
Timeline image is defined with a fixed height and width.
When the timeline loads it determines the size of items
then uses this to place them, as the images won't be 
loaded at this point the size must be set to ensure the 
spacing is correct
*/
.timeline-image {
  height: 40px;
  width: 40px
}

JavaScript

// DOM element where the Timeline will be attached
var container = document.getElementById("visualization");

// Create a DataSet (allows two way data-binding)
var items = new vis.DataSet();

items.add([
  { id: 1, content: "item 1", start: "2021-12-21", end: "2021-12-23", imageColor: "0000FF" },
  { id: 2, content: "item 2", start: "2021-12-14", end: "2021-12-17", imageColor: "FFFFFF" },
  { id: 3, content: "item 3", start: "2021-12-18", end: "2021-12-20", imageColor: "0000FF" },
  { id: 4, content: "item 4", start: "2021-12-16", end: "2021-12-21", imageColor: "FFFFFF" },
  { id: 5, content: "item 5", start: "2021-12-25", end: "2021-12-27", imageColor: "000000" },
  { id: 6, content: "item 6", start: "2021-12-27", end: "2021-12-28", imageColor: "008000" },
]);

// Configuration for the Timeline
var options = {
  // Define a template function which constructions the HTML for each item
  template: function (item, element, data) {
    var html = "<img class='timeline-image' src='https://via.placeholder.com/40/" + item.imageColor + "'><div>" + item.content + "</div>"
    return html;
  },
  // Using a template requires any properties to be whitelisted to prevent XSS
  // More details at https://github.com/visjs/vis-timeline/pull/1010
  xss: {
    disabled: false,
    filterOptions: {
      whiteList: { img: ['src', 'class'], div: 'class' }
    },
  },
};

// Create a Timeline
var timeline = new vis.Timeline(container, items, options);