[рони]

Artur_Hopf,

<style type="text/css">
.block{position:absolute;left:50%;top:50%;}
#back{position:absolute;left:50%;top:80%;}</style>
<script type="text/javascript" src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
<button class="block">Жми</button>
<button id ="back">Вернуть на место</button>
<script type="text/javascript">
$('.block').click(function(){
        $(".block").css({ "left": "30%","top": "20%"});
});
$('#back').click(function(){
        $(".block").removeAttr("style");
});
</script>