Hello fosiul,
By default, OpenLayers uses Web Mercator Projection ([EPSG:3857][1]).
So you cannot use Longitude, Latitude directly to set the center.
This is what you should use :
view: new ol.View({
maxZoom: 25,
center: ol.proj.fromLonLat([23.75936, 90.37787]),
ol.proj.fromLonLat([90.37787,23.75936]),
zoom: 9
})
More documentation on ol.proj : [http://openlayers.org/en/latest/apidoc/ol.proj.html][2]
[1]: http://epsg.io/3857
[2]: http://openlayers.org/en/latest/apidoc/ol.proj.html