Question

Is there a way to make a div appear half off-screen using just CSS without knowing the width of the div?

Answer 1

Unless I’ve misunderstood the question, I think it is possible with CSS, as I hope should be clear from this jsfiddle.

Example HTML

<div class="container one">
   <div class="half">Hello there.</div>
</div>
   <div class="container two">
<div class="half">Hello there, you old dog.</div>
   </div>
<div class="container three">
   <div class="half">Hello there you old dog. Been up to your old tricks?</div>
</div>

The CSS

.container {
    position: absolute;
}
.half {
    position: relative;
    right: 50%;
}
.two {
    top: 30px;
}
.three {
    top: 60px;
}