body {
  background-image: url("blog_background.jpg");
}

.background {
  margin-top: 30px;
  margin-right: 85px;
  margin-left: 75px;
  position: fixed;
  height: 100%;
  background-color: white;
  border: 2px solid #d3d3d3;
  border-radius: 20px;
  border-bottom: -50px;
  padding-top: 5px;
  padding-left: 5px;
  padding-right: 5px;
}

.background:before {
   content: " ";
   border-radius: 20px;
   position: fixed;
   z-index: -1;
   top: 22px;
   left: 60px;
   right: 70px;
   height: 100%;
   border: 1px solid white;
   background-color: white;
}
body {
  background-image: url("blog_background.jpg");
}

.background {
  margin-top: 30px;
  margin-right: 85px;
  margin-left: 75px;
  position: fixed;
  height: 100%;
  background-color: white;
  border: 2px solid #d3d3d3;
  border-radius: 20px;
  border-bottom: -50px;
  padding-top: 5px;
  padding-left: 5px;
  padding-right: 5px;
}

.background:before {
   content: " ";
   border-radius: 20px;
   position: fixed;
   z-index: -1;
   top: 22px;
   left: 63px;
   right: 70px;
   height: 100%;
   border: 1px solid white;
   background-color: white;
}
Update left border in CSS
Update left border in CSS
