Tips for a back-end guy to style my webapp

How would I, a back-end guy (that lacks creativity and passion for front-end), can make my webapp look at least proper and a little bit responsive through screen sizes? Any tips/good resources that I can learn a few key things quick just to get the job done? My site’s server-side functionality and some front-end logic is almost done so, I just need itsy bitsy things here and there to give some styling before I finally get it up and running!

Use a style library such as Material Design, Antd, Bootstrap, etc. Out of the box they will look pretty generic and give you expected responsiveness and behavior.