<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
* {
box-sizing: border-box;
}
.button-origin {background-color:#fff;font-size:14px;color:#000;padding:6px 13px;border:1px solid #ccc;border-radius:3px;display:block;text-align:center;max-width:100%;padding:15px 0;font-size:20px;font-weight:400;margin-left:70%;position: relative;
}
.spoiler_body {display:none;cursor:default;position:absolute;border: solid 1px #ececec;padding:10px; z-index:101;background-color: #fff;color:#333333;box-sizing:border-box;box-shadow:0px 0px 4px 1px #eee;-webkit-box-shadow:0px 0px 4px 1px #eee;-moz-box-shadow:0px 0px 4px 1px #eee;width:auto;margin:auto;left:0;right:0;margin-top:45px;font-size:14px;}
.spoiler_body.open{
display: inline-block; word-wrap: break-word;
}
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
$(function() {
$(".button-origin").on("click", function() {
$(".spoiler_body").addClass("open");
});
$("html").on("click", function(event) {
$(event.target).closest(".spoiler_body, .button-origin").length || $(".spoiler_body").removeClass("open");
});
});
</script>
</head>
<body>
<div class="button-origin button">
<span>Оставить сообщение</span>
<div class="spoiler_body">Чтобы отправить сообщение необходимо войти или зарегистрироваться
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</body>
</html>