Tooltips
Add tooltips built entirely in CSS to nearly any element. Just add a few classes and an aria-label attribute.
In addition, you’ll want to specify a direction:
.tooltipped-n.tooltipped-ne.tooltipped-e.tooltipped-se.tooltipped-s.tooltipped-sw.tooltipped-w.tooltipped-nw
Remember, aria-label and tooltip classes must go directly on <button> and <a> elements. Tooltip classes also conflict with Octicon classes, and as such, must go on a parent element instead of the icon.
Text with a tooltip
<span class="tooltipped tooltipped-n" aria-label="This is the tooltip.">
Text with a tooltip
</span>