How do I align a button to the bottom center? - css

Question

I have a responsive design with 4 fluid blocks.
I want the submit button to be fixed at bottom center.
The problem is, the button is shifted to the right (but not perfectly right-aligned)
Here is my css:
#product-list{
width: 100%;
padding: 0 40px;
margin: 30px 0 0 0;
position:relative;
}
article.products{
float: left;
position:relative;
width: 24%;
margin-top: 5px;
margin-bottom: 5px;
margin-right: 0;
text-align: center;
border: 1px solid #C0C0C0;
-webkit-border-radius: 5px;
-moz-border-radius: 5px;
-ms-border-radius: 5px;
-o-border-radius: 5px;
border-radius: 5px;
padding: 10px;
background: #fbfbfb;
background-image: -ms-radial-gradient(center, ellipse farthest-corner, #FFFFFF 90%, #EFEFEF 100%);
background-image: -moz-radial-gradient(center, ellipse farthest-corner, #FFFFFF 90%, #EFEFEF 100%);
background-image: -o-radial-gradient(center, ellipse farthest-corner, #FFFFFF 90%, #EFEFEF 100%);
background-image: -webkit-gradient(radial, center center, 0, center center, 506, color-stop(.90, #FFFFFF), color-stop(1, #EFEFEF));
background-image: -webkit-radial-gradient(center, ellipse farthest-corner, #FFFFFF 90%, #EFEFEF 100%);
background-image: radial-gradient(ellipse farthest-corner at center, #FFFFFF 90%, #EFEFEF 100%);
}
article.products input[type="submit"] {
position: absolute;
bottom: 5px;
left: 50%;
}
Here is the html (deleted unnecessary code; it is a dynamic loop for the boxes):
<div id="product-list">
<section class="main">
<article class="products">
<input name="Submit" type="Submit">
</article>
</section>
</div>

Answer 1

You have to place the input in a parent div
<div class="parent_div">
<input name="Submit" type="Submit">
</div>
And use this CSS to arrange it
.parent_div {
position: absolute;
bottom: 5px;
width: 100%;
}
.parent_div input {
margin: 0 auto;
}

Answer 2

So yeah here is your code:
article.products input[type="submit"] {
margin-left: 50%;
margin-right: 50%;
marging-bottom: 5px;
}
Or you could put a padding-bottom: 5px to the container class. Your choice.