Rounding Corners on WordPress Content Section

https://www.w3schools.com/cssref/tryit.asp?filename=trycss3_border-radius

Ya. I know how to round corners with CSS, but what would I point it to with my stylesheet? Like…

NAMEHEREIDK
{
border-radius:25px;
}

Do you have Google Chrome?

Yes

View your webpage in Google Chrome,
Right click on the element you want to style,
Select ‘Inspect element’,
A new toolbar appears. Look at the right column for the CSS selectors.

Use those CSS selectors to target your styles.