Add a tooltip to a div

For the basic tooltip, you want:

<div title="This is my tooltip">

like:

.visible {
  height: 3em;
  width: 10em;
  background: yellow;
}

<div title="This is my tooltip" class="visible"></div>

For a fancier javascript version, you can look into:

https://jqueryhouse.com/best-jquery-tooltip-plugins/

The above link gives you 25 options for tooltips.

It can be done with CSS only, no javascript at all

running demo

[data-tooltip]:before {
    /* needed - do not touch */
    content: attr(data-tooltip);
    position: absolute;
    opacity: 0;
    
    /* customizable */
    transition: all 0.15s ease;
    padding: 10px;
    color: #333;
    border-radius: 10px;
    box-shadow: 2px 2px 1px silver;    
}

[data-tooltip]:hover:before {
    /* needed - do not touch */
    opacity: 1;
    
    /* customizable */
    background: yellow;
    margin-top: -50px;
    margin-left: 20px;    
}

[data-tooltip]:not([data-tooltip-persistent]):before {
    pointer-events: none;
}

/* FOR TEST PURPOSES ONLY */
div {
    border: 1px solid silver;
    background: #ddd;
    margin: 20px;
    padding: 10px;
}

<div>Standard div, no tooltip here</div>


<div data-tooltip="Hi, I'm a tooltip. Pretty easy uh ? ;)">Div with standard tooltip. Hover me to see the tooltip.
    <br/>Hovering the tooltip doesn't matter:
    <br/>if you hover out of my boundaries, the tooltip will disappear.</div>


<div data-tooltip="Hi, I'm a persistent tooltip. I won't disappear when hovering me even if out of my parent boundaries. I'll also prevent other tooltips to fire :)" data-tooltip-persistent="foo">Div with persistent tooltip. Hover me to see the tooltip.
    <br/>The tooltip won't expire until you hover on me OR it.</div>

1. Apply a custom HTML attribute, eg. data-tooltip="bla bla" to your object (div or whatever):

    <div data-tooltip="bla bla">
        something here
    </div>
   

2. Define the :before pseudoelement of each [data-tooltip] object to be transparent, absolutely positioned and with data-tooltip="" value as content:

    [data-tooltip]:before {            
        position : absolute;
         content : attr(data-tooltip);
         opacity : 0;
    }
   

3. Define :hover:before hovering state of each [data-tooltip] to make it visible:

    [data-tooltip]:hover:before {        
        opacity : 1;
    }
   

4. Apply your styles (color, size, position etc) to the tooltip object; end of the story.

In the demo I've defined another rule to specify if the tooltip must disappear when hovering over it but outside of the parent, with another custom attribute, data-tooltip-persistent, and a simple rule:

[data-tooltip]:not([data-tooltip-persistent]):before {
    pointer-events: none;
}

Note 1: The browser coverage for this is very wide, but consider using a javascript fallback (if needed) for old IE.

Note 2: an enhancement might be adding a bit of javascript to calculate the mouse position and add it to the pseudo elements, by changing a class applied to it.