python/strava-leaflet-app/templates/leaflet.html

<html>
  <head>
    <title>Mapping my runs</title>
	<link rel="stylesheet"
		  href="https://unpkg.com/leaflet@1.9.4/dist/leaflet.css"
		  integrity="sha256-p4NxAoJBhIIN+hmNHrzRCf9tD/miZyoHS5obTRR9BMY="
		  crossorigin=""/>
  </head>

  <body>
	<script src="https://unpkg.com/leaflet@1.9.4/dist/leaflet.js"
			integrity="sha256-20nQCchB9co0qIjJZRGuk2/Z9VM+kNiyxNV1lvTlZBo="
			crossorigin=""></script>
    <script type="text/javascript"
			src="https://rawgit.com/jieter/Leaflet.encoded/master/Polyline.encoded.js"></script>
    <div id="map" style="height: 500px"></div>

    <script>
    var map = L.map("map").setView([50.73140, 3.07874], 11);
    L.tileLayer(
        "http://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png", {
            maxZoom: 18,
			attribution: "&copy; <a href=\"http://www.openstreetmap.org/copyright\">OpenStreetMap</a>"
        }).addTo(map);

    var encodedRoutes = {{ runs|safe }};

    for (let encoded of encodedRoutes) {
      var coordinates = L.Polyline.fromEncoded(encoded).getLatLngs();

      L.polyline(
          coordinates,
          {
              color: "blue",
              weight: 2,
              opacity: .7,
              lineJoin: "round"
          }
      ).addTo(map);
    }
    </script>
  </body>
</html>