The BF_Tags_HTML custom function takes an optional CSS parameter. If you would like to change the styling of the widget, you can create your own css and pass it in there.
These are the classes used in the widget
|Class||Where it is used|
|Body||the main body of the web viewer|
|.tagsinput||the div surrounding the entire functional part of the widget|
|.tag||the div that surrounds the tag label and the remove button if it is displayed|
|.tag .remove||the styling of the remove button|
|.form||the styling of the div surrounding the tag entry field|
|.form .forminput||the styling of the tag entry field itself|
|.form ::placeholder||the styling of the placeholder text in the tag entry field|
The easiest way to make your own custom css is to duplicate the BF_Tags_CSS custom function and simply edit the css found there.