put a HTML element over a map tile

When I was working with ember-leaflet v2.2.7, the HTML elements were displayed over the map tiles like in the picture below, but in the version 3.0.11 the map is in the front.

Setting the z-index of the leaflet-container element to -1 the map is pushed to the back but the map is inaccessible, I mean, the map cannot be zoom-in/out or the tooltip of the marker is not displayed when it is tapped.

In v3.0.11 the button element is like hidden, I mean when the map tiles are loading the button is visible (see picture below) but when the tiles are loaded the button disappears but if it's location is tapped the action related with the button is triggered.