h1 {
/* A nice big spacing so you can see the effect */
letter-spacing: 1em;
/* we need relative positioning here so our pseudo element stays within h1's box */
position: relative;
/* centring text throws up another issue, which we'll address in a moment */
text-align: center;
/* the underline */
text-decoration: underline;
}
h1:after {
/* absolute positioning keeps it within h1's relative positioned box, takes it out of the document flow and forces a block-style display */
position: absolute;
/* the same width as our letter-spacing property on the h1 element */
width: 1em;
/* we need to make sure our 'mask' is tall enough to hide the underline. For my own purpose 200% was enough, but you can play and see what suits you */
height: 200%;
/* set the background colour to the same as whatever the background colour is behind your element. I've used a red box here so you can see it on your page before you change the colour ;) */
background-color: #990000;
/* give the browser some text to render (if you're familiar with clearing floats like this, you should understand why this is important) */
content: ".";
/* hide the dynamic text you've just added off the screen somewhere */
text-indent: -9999em;
/* this is the magic part - pull the mask off the left and hide the underline beneath */
margin-left: -1em;
}
<h1>My letter-spaced, underlined element!</h1>