All solutions

Thank you for the assistance everyone! I believe this one is solved. Once I was made aware of media queries I was able to solve the issue of the rounded corners appearing and disappearing. Any further tips on styling and general code etiquette is much appreciated! Just so I can formally get my head around media queries but as I understand it:

@media (max-width: 600px) {
              /*Insert CSS style that changes*/
}

Would mean once the page dips below 600px the styling inside takes effect?

Cheers all!

Updated solution trying to incorporate suggested fixes. I have still go no idea on the size of the project soooooo I mightve eyeballed it :D.

Cheers.