Button-groups at the bottom in differents devices - html

Question

I am doing a design for mobile and I have to think in differents devices. I put a button-group in bottom of the page. It's means the bottons appear at the final of the scroll-bar. But, when the page its too small because the device is big, the bottons appear at the middle of the page. And after that, there is white space.
I try with this rules: How to put the footer at the bottom of the visible page? But the buttons appear always at the bottom of the screen. I need see the bottons after using scroll-bar.
HTML
<div id="botoneraInternet" class="btn-group btn-group-justified" role="group" aria-label="...">
<div class="btn-group btn-group-lg" role="group">
<button type="button" class="btn btn-default" id="botonHardware" disabled="" style="background-color: rgb(48, 144, 184);">
<span><img class="icons" src="imagenes/llave.png"></span> Hardware
</button>
</div>
<div class="btn-group btn-group-lg" role="group">
<button type="button" class="btn btn-default" id="botonClose" style="background-color: rgb(223, 228, 229);">
<span><img class="icons" src="imagenes/valija.png"></span> Cerrar WO
</button>
</div>
</div>
CSS
.btn-group {
position: relative;
vertical-align: middle;
}
.btn-group-justified {
display: table;
width: 100%;
table-layout: fixed;
border-collapse: separate;
}
Someone can help me?
Really thanks, and I am going to give the star to the best answer.

Answer 1

try this....there wasn't enought code you provided so I improvised a bit. But let me know if this is what you need.
http://codepen.io/carinlynchin/pen/WvbLXE
CSS:
body{
height:900px;
position:relative;
}
.btn-group {
position: absolute;
width:100%;
bottom:0
}
.btn-group div {
display:inline;
}
HTML:
<div id="botoneraInternet" class="btn-group btn-group-justified" role="group" aria-label="...">
<div role="group">
<button type="button" class="btn btn-default" id="botonHardware" disabled="" style="background-color: rgb(48, 144, 184);">
<span><img class="icons" src="http://barkpost-assets.s3.amazonaws.com/wp-content/uploads/2013/11/grumpy-dog-11.jpg"></span> Hardware
</button>
</div>
<div role="group">
<button type="button" class="btn btn-default" id="botonClose" style="background-color: rgb(223, 228, 229);">
<span><img class="icons" src="https://pbs.twimg.com/profile_images/3540744128/7dd80644ae052f1b04180c41bbc674ab.png"></span> Cerrar WO
</button>
</div>
</div>