I am trying to use the
<span class="mystyle">buuu!</span>a some more
<input class="mystyle" type="text" value="someValue">
:before are not supported in Internet Explorer 7 and under, on any elements.
It's also not meant to be used on replaced elements such as form elements (inputs) and image elements.
In other words it's impossible with pure CSS.
However if using jquery you can use
$(".mystyle").after("add your smiley here");