<div class='holder'>
<div class='block'>какой-то текст</div>
<div class="html"><button> нопка</button></div>
<style>
.holder{
position:relative;
padding:20px;
width:100px;
height:50px;
border: #000000 solid 1px;
}
.html{
position:absolute;
left:0;
top:0;
right:0;
display:none;
}
.holder:hover .html{
display:block;
padding:20px;
}
.holder:hover .block{
display:none;
}
</style>