When you create a new application with Mendix, there are quite some Templates to choose from
In addtion, Within Mendix tudio Pro 9.* and higher, you can set the basis styling for colors, positioning and animation either on the pages. Width Mendix Studio Pro 9,24 and higher you can install the UI Resource module, which allows you to fully embracre (s)css. I have not found any limitations in styling. I also run a website on Mendix, and completely styled it with just the UI Resource module.
Could you please tell me what it is you miss in order to make an awesome UX with Mendix?