move invisible tooltip to top left corner to prevent layout shift (#277)

The tooltip is placed at the bottom of the body which makes the page
slightly longer, even though the user can't see the content. This might
result in a layout shift when the tooltip is displayed for the first
time and the scrollbar disappears.

Move the invisible tooltip element to the top-left corner fixes this
issue. We use left/top CSS properties, because these two will be
dynamically overwritten on mouse events anyway.

css/dashboard.css

@@ -42,7 +42,9 @@ body.rtl #statify_chart * {
 	border: 1px solid #000;
 	background-color: #fff;
 	border-radius: 0.2em;
+	left: 0;
 	padding: 0.1em 0.5em;
+	top: 0;
 }
 
 .statify-chartist-tooltip::before {