I think the default style (even of the demo on the page) should be no style.
It also comes with a number of themes to help match other UI frameworks. See the themeing examples here: http://tabulator.info/examples/4.1#theming
As well as built in themes it comes with extensive documentation on the CSS classes as well as overrideable SASS variables for all themes to make customising as easy as possible, more information can be found in the styling documentation: http://tabulator.info/docs/4.1/style
each theme is contained in its own CSS file, you simply include the CSS file for the theme of your choice.
Configuring themes for your table is covered extensively in the documentation along with examples of each theme in use: http://tabulator.info/docs/4.1/theme