https://developer.mozilla.org/ko/docs/Web/CSS/filter-function/blur()

html

    <section class="bg"></section>
    <div class="loading-text">0%</div>

css

@import url('https://fonts.googleapis.com/css?family=Ubuntu');

* {
  box-sizing: border-box;
}

body {
  font-family: 'Ubuntu', sans-serif;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  overflow: hidden;
  margin: 0;
}

.bg {
  background: url('사진링크')
    no-repeat center center/cover;
  position: absolute;
  top: -30px;
  left: -30px;
  width: calc(100vw + 60px);
  height: calc(100vh + 60px);
  z-index: -1;
  filter: blur(0px); /*70px로 효과 체크*/
}

.loading-text {
  font-size: 50px;
  color: #fff;
}