See the question and my original answer on StackOverflow

Here is a 100%-CDN HTML sample page with latest versions of Sigma + Graphology + Force Atlas 2. Note I'm using javascript modules and import maps, which may not be supported by all browsers:

<!doctype html>
<html lang="en">

<head>
  <meta charset="UTF-8" />
  <title>Sigma.js + Graphology.js example</title>
  <script type="importmap">
      {
        "imports": {
          "sigma": "https://cdnjs.cloudflare.com/ajax/libs/sigma.js/3.0.0/sigma.min.js",
          "graphology": "https://cdn.jsdelivr.net/npm/graphology@0.26.0/dist/graphology.umd.min.js",
          "graphologyLibrary": "https://cdn.jsdelivr.net/npm/graphology-library/dist/graphology-library.min.js"
        }
      } 
    </script>
</head>

<body style="background: lightgrey">
  <div id="container" style="width: 600px; height: 600px; background: white"></div>
  <script type="module">
    import * as sigma from 'sigma';
    import 'graphology'; // has no exports, import all
    import 'graphologyLibrary'; // has no exports, import all

    // Create a graphology.js graph, use random to init the graph
    const graph = new graphology.Graph()
    graph.addNode("1", { label: "Node 1", x: Math.random(), y: Math.random(), size: 10, color: "red" });
    graph.addNode("2", { label: "Node 2", x: Math.random(), y: Math.random(), size: 15, color: "green" });
    graph.addNode("3", { label: "Node 3", x: Math.random(), y: Math.random(), size: 20, color: "blue" });
    graph.addEdge("1", "2", { size: 5, color: "purple" });
    graph.addEdge("1", "3", { size: 5, color: "purple" });
    graph.addEdge("2", "3", { size: 5, color: "purple" });

    // Infer settings from graph & assign
    const settings = graphologyLibrary.layoutForceAtlas2.inferSettings(graph);
    graphologyLibrary.layoutForceAtlas2.assign(graph, {
      iterations: 50,
      settings: settings
    });

    // Instantiate sigma.js and render the graph
    const s = new Sigma(graph, document.getElementById("container"));
  </script>
</body>

</html>

Sigma + Graphology + Force Atlas 2