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<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.sidebar{
background-image: url(https://s.poembook.ru/theme/a9/c9/09/8393d39722f905841f4dc46d8c4e7babb1f9e067.jpeg);
background-size: contain;
background-repeat: no-repeat;
}
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<script>
$(function() {
var url = "https://s.poembook.ru/theme/a9/c9/09/8393d39722f905841f4dc46d8c4e7babb1f9e067.jpeg";
var img = new Image;
img.onload = function() {
$(".sidebar").height(this.height);
};
img.src = url;
});
</script>
</head>
<body>
<div id="secondary" class="sidebar" ></div>
</body>
</html>