style.css

html, body {
    margin:0;
    padding:0;
    height:100%;
}
#map{
    margin:0;
    padding:0;
    width:100%;
    height:100%;
}
.leaflet-label {
    background: rgb(235, 235, 235);
    background: rgba(235, 235, 235, 0.81);
    background-clip: padding-box;
    border-color: #777;
    border-color: rgba(0,0,0,0.25);
    border-radius: 4px;
    border-style: solid;
    border-width: 4px;
    color: #111;
    display: block;
    font: 12px/20px "Helvetica Neue", Arial, Helvetica, sans-serif;
    font-weight: bold;
    padding: 1px 6px;
    position: absolute;
    -webkit-user-select: none;
       -moz-user-select: none;
        -ms-user-select: none;
            user-select: none;
    white-space: nowrap;
    z-index: 6;
}

.leaflet-label:before {
    border-right: 6px solid black;
    border-right-color: inherit;
    border-top: 6px solid transparent;
    border-bottom: 6px solid transparent;
    content: "";
    position: absolute;
    top: 5px;
    left: -10px;
}