code: function css(prop, value){
    if (value) {
      this.style(prop, value);
    } else {
      const that = this;
      Object.keys(prop).map(function(o,i) {
        const value = prop[o];
        that.style(o, value);
      });
    }
    return this;
  }
docs: jQuery equivalent: [$.css](http://api.jquery.com/css/)
  
  Applies style to elements in the current selection. Returns the selection.
  Works in the same way like the D3 style function we only changed the name here.
  
  @function css
  @example
  selection.css(name, value);
  selection.css(object);
  
  @returns {selection} - The current selection