I do not know what your level of knowledge is in SASS and CSS(since this are the things mendix uses), but there are multiple themes and styling options.
It is possible to make your own stylesheets and use them in mendix studio pro at system > settings > theme.
However I would firstly recommend this learning path:
https://gettingstarted.mendixcloud.com/link/path/56
Further you can take a look at calypso: