Academica nav header color will not change

https://www.rogierwolf.nl/

Hello, I’m trying to adjust the colour off the main navigation in my childtheme. The main nav can be found in CSS line 471. As I change the colour from #2A678D into bright blue #4169e1 and upload the new CSS to my childtheme….nothing happens.

#main-nav ul {
background-color: #3A678D;
display: inline-block;
font-size: 12px;
font-weight: bold;
line-height: 1.8;
margin-bottom: 20px;
margin-left: 0;
margin-right: 0;
margin-top: 0;
position: relative;
width: 100%;
z-index: 300;
}

Any suggestions please?

Thanks in advance!