Customize Zoom in/out button in leaflet.js

Your zoom in/out controls are wrapped with absolutely positioned element with left:0 (due to .leaflet-left class), so float:left wouldn’t help, you could align it to right by overriding left:0 by right:0, or changing .leaflet-left class to .leaflet-right

But more correct way would be to use provided api.

//disable zoomControl when initializing map (which is topleft by default)
var map = L.map("map", {
    zoomControl: false
    //... other options
});

//add zoom control with your options
L.control.zoom({
     position:'topright'
}).addTo(map);

see updated fiddle

api reference for the library you use can be found here