This is not possible with css, but I have used one css trick in one of my website, please check if this works for you.
The trick is: wrap the input box with a div and make it relative, place a transparent image inside the div and make it absolute over the input text box, so that no one can edit it.
css
.txtBox{
width:250px;
height:25px;
position:relative;
}
.txtBox input{
width:250px;
height:25px;
}
.txtBox img{
position:absolute;
top:0;
left:0
}
html
<div class="txtBox">
<input name="" type="text" value="Text Box" />
<img src="http://dev.w3.org/2007/mobileok-ref/test/data/ROOT/GraphicsForSpacingTest/1/largeTransparent.gif" width="250" height="25" alt="" />
</div>