HTML: 1-pixel horizontal line

<div> element is quite useful for creating 1-pixel width horizontal lines on Web page. For example, we can use empty DIV container and than write the following CSS style:
.separator {
height: 1px;
width: 90%;
display: block;
background-color: #555555;
margin-left: auto;
margin-right: auto;
}
This works fine everywhere except IE6. It creates a horizontal line with minimum width equal to the current font size:

The hack for IE6 is adding empty comment to the div:
<div class="separator"><!----></div>

The result is the same in all browsers:


P.S. "font-size: 1px" doesn't do the trick because, all the same, the resulting line is 2px or something