My First Deployed Project: Text Message Scheduler

I've been browsing and lurking on this site for a while and have been really inspired by many of the projects and startups that people have built. Although it's quite simple, I wanted to share my first solo project http://www.ticktock.fun and would love any feedback.

The app is a simple Text message scheduler (set a time & date and you'll receive a text message reminding you of something).

I'm a recent entrant into the world of coding so this is my first solo coded project and would love to to hear any feedback!

Here is the stack I used to build it: ReactJS/ExpressJS/NodeJS/MongoDB/AWS

Although the project itself only took a couple days, I actually spent 90% of the time dealing with HTML & CSS (CSS in particular) trying to make everything line up and then ultimately render (decently) on mobile; I would really appreciate any tips, tricks, tools, etc to get the CSS looking nice and mobile friendly if you happen to have them (e.g., libraries, frameworks or anything else). Thanks!