SOURCE

<main>
  <blockquote>
    “yangzhicaho”
    <footer>
      —
      <cite>
        Oscar Wilde, The Picture of Dorian Gray
      </cite>
    </footer>
  </blockquote>
</main>

body, main::before {
  background: url("https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1529383164806&di=d4b00602bc99f5b5b72f07eb6db84090&imgtype=jpg&src=http%3A%2F%2Fimg0.imgtn.bdimg.com%2Fit%2Fu%3D3564877025%2C796183547%26fm%3D214%26gp%3D0.jpg") 0 / cover fixed;
}

main {
  position: relative;
  top: 300px;
  width: 50%;
  left: 30%;
  background: hsla(0, 0%, 100%, .3);
  overflow: hidden;
}

main::before {
  /* background: rgba(255,255,255,0.3); */
  content: '';
  position: absolute;z-index: -1;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  filter: blur(10px);
  margin: -30px;
}