CSS on polylines

HTML

<script src="http://cdn.leafletjs.com/leaflet-0.7.5/leaflet.js"></script>
<link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet-0.7.5/leaflet.css">
<div id="map"></div>

CSS

#map { height: 300px; }

.my_polyline { 
 stroke: green;
  fill: none;
  stroke-dasharray: 5,5; 
  stroke-width: 10;  
}

JavaScript

// create a map in the "map" div, set the view to a given place and zoom
var map = L.map('map').setView([48.858190, 2.294470], 16);

// add an OpenStreetMap tile layer
L.tileLayer('http://{s}.tile.osm.org/{z}/{x}/{y}.png', {
    attribution: '&copy; <a href="http://osm.org/copyright">OpenStreetMap</a> contributors'
}).addTo(map);


var latlngs = [
    [51.509, -0.08],
    [51.503, -0.06],
    [51.51, -0.047],
    [51.509, -0.08]
];

// create a red polyline from an array of LatLng points
var polyline = L.polyline(latlngs, { className: 'my_polyline' }).addTo(map);

// zoom the map to the polyline
map.fitBounds(polyline.getBounds());