Adjust app sidebar title background color

Signed-off-by: Raimund Schlüßler <raimund.schluessler@mailbox.org>

Author: raimund-schluessler

css/src/style.scss

@@ -844,7 +844,7 @@ $blue_due: #4271a6;			// due dates and low importance
 			flex: 0 0 auto;
 			display: flex;
 			align-items: center;
-			background-color: var(--color-background-dark);
+			background-color: var(--color-background-hover);
 			border-bottom: 1px solid var(--color-border-dark);
 			font-size: 16px;
 			font-weight: bold;