color, weight. Enable Leaflet. Keep #map { height: 320px } in CSS.

Goal

Run every block and confirm the chart is visible.

<div id="map"></div>

#map { height: 320px; width: 100%; }

const map = L.map("map").setView([-1.5, 37], 6);
L.tileLayer("https://tile.openstreetmap.org/{z}/{x}/{y}.png", { attribution: "© OSM" }).addTo(map);
L.polyline([[-1.29,36.82],[-4.04,39.67]], { color: "#c45c26", weight: 4 }).addTo(map);
console.log("style");

<div id="map"></div>

const map = L.map("map").setView([-1.29, 36.82], 6);
L.tileLayer("https://tile.openstreetmap.org/{z}/{x}/{y}.png", { attribution: "© OSM" }).addTo(map);
L.marker([-1.29, 36.82]).addTo(map);
console.log("marker");