HTML-Tooltip position relative to mouse pointer

One way to do this without JS is to use the hover action to reveal a HTML element that is otherwise hidden, see this codepen:

http://codepen.io/c0un7z3r0/pen/LZWXEw

Note that the span that contains the tooltip content is relative to the parent li. The magic is here:

ul#list_of_thrones li > span{
  display:none;
}
ul#list_of_thrones li:hover > span{
  position: absolute;
  display:block;
  ...
}

As you can see, the span is hidden unless the listitem is hovered over, thus revealing the span element, the span can contain as much html as you need. In the codepen attached I have also used a :after element for the arrow but that of course is entirely optional and has only been included in this example for cosmetic purposes.

I hope this helps, I felt compelled to post as all the other answers included JS solutions but the OP asked for a HTML/CSS only solution.

You can use jQuery UI plugin, following are reference URLs

• http://jqueryui.com/tooltip/
• http://bassistance.de/jquery-plugins/jquery-plugin-tooltip/
• http://jquery-plugins.bassistance.de/tooltip/demo/

Set track to TRUE for Tooltip position relative to mouse pointer eg.

$('.tooltip').tooltip({ track: true });

For default tooltip behavior simply add the title attribute. This can't contain images though.

<div title="regular tooltip">Hover me</div>

Before you clarified the question I did this up in pure JavaScript, hope you find it useful. The image will pop up and follow the mouse.

jsFiddle

JavaScript

var tooltipSpan = document.getElementById('tooltip-span');

window.onmousemove = function (e) {
    var x = e.clientX,
        y = e.clientY;
    tooltipSpan.style.top = (y + 20) + 'px';
    tooltipSpan.style.left = (x + 20) + 'px';
};

CSS

.tooltip span {
    display:none;
}
.tooltip:hover span {
    display:block;
    position:fixed;
    overflow:hidden;
}

Extending for multiple elements

One solution for multiple elements is to update all tooltip span's and setting them under the cursor on mouse move.

jsFiddle

var tooltips = document.querySelectorAll('.tooltip span');

window.onmousemove = function (e) {
    var x = (e.clientX + 20) + 'px',
        y = (e.clientY + 20) + 'px';
    for (var i = 0; i < tooltips.length; i++) {
        tooltips[i].style.top = y;
        tooltips[i].style.left = x;
    }
};

I prefer this technique:

function showTooltip(e) {
  var tooltip = e.target.classList.contains("tooltip")
      ? e.target
      : e.target.querySelector(":scope .tooltip");
  tooltip.style.left =
      (e.pageX + tooltip.clientWidth + 10 < document.body.clientWidth)
          ? (e.pageX + 10 + "px")
          : (document.body.clientWidth + 5 - tooltip.clientWidth + "px");
  tooltip.style.top =
      (e.pageY + tooltip.clientHeight + 10 < document.body.clientHeight)
          ? (e.pageY + 10 + "px")
          : (document.body.clientHeight + 5 - tooltip.clientHeight + "px");
}

var tooltips = document.querySelectorAll('.couponcode');
for(var i = 0; i < tooltips.length; i++) {
  tooltips[i].addEventListener('mousemove', showTooltip);
}

.couponcode {
    color: red;
    cursor: pointer;
}

.couponcode:hover .tooltip {
    display: block;
}

.tooltip {
    position: absolute;
    white-space: nowrap;
    display: none;
    background: #ffffcc;
    border: 1px solid black;
    padding: 5px;
    z-index: 1000;
    color: black;
}

Lorem ipsum dolor sit amet, <span class="couponcode">consectetur
adipiscing<span class="tooltip">This is a tooltip</span></span>
elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi
ut aliquip ex ea commodo consequat. Duis aute irure dolor in <span
class="couponcode">reprehenderit<span class="tooltip">This is
another tooltip</span></span> in voluptate velit esse cillum dolore eu
fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident,
sunt in culpa qui officia deserunt mollit anim id est <span
class="couponcode">laborum<span class="tooltip">This is yet
another tooltip</span></span>.

(see also this Fiddle)