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CSS
HTML
Result

body {
  background: lightblue url("http://ezcode.kr/study/css/img/tree.gif") no-repeat fixed right center/contain;
}

<!DOCTYPE html>
<html lang="ko">
  <head></head>
  <body>
    <h1>background</h1>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
    <p>This is some text</p>
  </body>
</html>