Why in IE7 input breaks out of its container?

<div class="row-fluid" style="margin-top:10px;">
<div class="span12">
<div class="row-fluid">
<div class="span6">
<div class="row-fluid">
<div class="span6 " style="background:green;">
<input type="text" class="span12">
</div>
<div class="span6" style="background:blue;">
<input type="text" class="span12">
</div>
</div>
</div>
<div class="span6">
<div class="row-fluid">
<div class="span6" style="background:green;">
<input type="text" class="span12">
</div>
<div class="span6" style="background:blue;">
<input type="text" class="span12">
</div>
</div>
</div>
</div>
</div>
</div>
UPDATE: I suppose it’s box-model and width issue, but is any solution with bootstrap?
this happens because IE7 does not support the css property
that considers padding and border size as part of the elements width.
read more about this property here: http://paulirish.com/2012/box-sizing-border-box-ftw/
because of this, IE7 adds the padding and border size to the input width – exceeding the parent width. You will have to set those to 0 in order to get the element fit to the parent size and stay fluid.
you could try adding a wrapper element around the input and then setting the padding and border to the wrapper. This will work in all browsers