Themes: explicitely set background and text color for tooltips

As the colors of QToolTip depend on the desktop environment used,
explicitely set background and text color for fixing cases like
white text on bright yellow background.

Closes #3006955.

data/themes/cusis/style.css

@@ -74,6 +74,11 @@ automationEditor {
 }
 
 
+QToolTip {
+	background: rgb(224,224,224);
+	color: black;
+}
+
 QMenu {
 	border:1px solid black;
 	background-color: rgb( 192, 192, 192 );

data/themes/default/style.css

@@ -45,6 +45,11 @@ automationEditor {
 }
 
 
+QToolTip {
+	background: rgb(224,224,224);
+	color: black;
+}
+
 QMenu {
 	border:1px solid black;
 	background-color: rgb( 192, 192, 192 );