app/assets/stylesheets/_fileinput.sass
.fileinput-button
position: relative
overflow: hidden
.fileinput-button input
position: absolute
top: 0
right: 0
margin: 0
opacity: 0
-ms-filter: 'alpha(opacity=0)'
font-size: 200px
direction: ltr
cursor: pointer
// Fixes for IE < 8
@media screen\9
.fileinput-button input
filter: alpha(opacity=0)
font-size: 100%
height: 100%