.ol-combined-flat{
    position: relative;
    border: 1px solid #ddd;
    background-color: #fff;
}

.ol-combined-flat > div{
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}

.ol-combined-flat [ol-flat-map] canvas{
    background-color: #fff;
}