If you aren't comfortable with using negative margins, check this out.
div {
position: fixed;
left: 50%;
bottom: 20px;
transform: translate(-50%, -50%);
margin: 0 auto;
}<div>
Your Text
</div>Especially useful when you don't know the width of the div.
align="center" has no effect.
Since you have position:absolute, I would recommend positioning it 50% from the left and then subtracting half of its width from its left margin.
#manipulate {
position:absolute;
width:300px;
height:300px;
background:#063;
bottom:0px;
right:25%;
left:50%;
margin-left:-150px;
}