Change Jupyter notebook version 4.x+ logo

So here is the quick solution thanks to @Eric comment (referring to this post). First, I add logo.png into .jupyter/custom/logo.png. Then add the following lines to .jupyter/custom/custom.css in order to load the logo.

#ipython_notebook img{                                                                                        
    display:block;
    /* logo url here */
    background: url("logo.png") no-repeat;
    background-size: contain;
    width: 233px;
    height: 33px;
    padding-left: 233px;
    -moz-box-sizing: border-box;
    box-sizing: border-box;
}

You can also add this css tag to increase logo padding height by adding:

#ipython_notebook {
    height: 40px !important;
}