Custom CSS for white-background on Widget

Hello,

Im using the WP Strava Plugin and is showing a Widget for our club.
As you can see under: http://www.osbycykelteam.se/lankar/

There is the Widget called rides, the text is in black which isnt to good on a gray background 🙂

I have tried alternating the CSS inserting the following:

.uk-panel-box {
	padding: 30px;
	background: #282e36;
	color: #FFFFFF;
	box-shadow: 0 0 0 0 rgba(0,0,0,0);
}

However it seems it is ignored 🙁
All your help would be deeply appriciated.

Best regards
Kenny