背景图片模糊

Question

我已经使用Bootstrap 4为自己开发了一个简单的Portfolio网站，一切正常只能解决一个问题。当我在Ipad或iphone上查看网站时，背景图片非常模糊。一个试图调整它的大小，但是没有用，请问如何解决这个问题？这是我的网站www.mmcodes.com和CSS文件

    /*************** REUSABLE **************/

html {
  -webkit-box-sizing: border-box!important;
          box-sizing: border-box!important;
}

body {
  font-family: "Lato", "Helvetica Neue",Helvetica,Arial,sans-serif;
  position: relative;
}


.navbar-brand, .nav-item{
  color: white!important;
  font-family: "Handlee", cursive;
  font-size: 1.3em;

}

#myNavbar .active  {
  color: #4a5e76 !important;
}


/************ HOME ***********************/

#section-home {
  background-image: url(../img/tech-min.jpg);
  background-size: cover;
  background-attachment: fixed;
  height: 100vw;
}

#section-home .intro-header {
  font-family: "Handlee", cursive;
  padding-top: 150px;
  padding-bottom: 50px;
  text-align: center;
  color: white;
  height: 650px;

}

#section-home h1 {
  margin-top: 90px;
}

#section-home hr {
  width: 400px;
  border-bottom: 1px solid rgba(0,0,0,0.2);
  border-top: 1px solid #f8f8f8;
}


#section-home ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
  display: inline;
}

li a{
  color: white!important;
  font-family: 'Handlee', cursive;
  padding-top: 10px;
}

#section-home .social-media-buttons > li {
  padding-top: 0px;
  text-align: center;
  display: inline;
  margin-left: 10px;
  margin-right: 10px;
  font-family: 'Handlee', cursive;
}

#section-home i {
  font-size: 20px;
}

#section-home #github i {
  font-size: 20px;
  padding-right: 7px;

}

#section-home li a {
  padding-top: 13px;

}

#section-home #github {
  padding-left: 18px;
  padding-right: 18px;
}


/******************** ABOUT **********************/
#section-about {
  padding-top:50px;
  padding-bottom: 100px;
  background-color: #e3e7ed;
}

#section-about h3 {
  text-decoration: underline;
  text-align: center;
  margin-top: 40px;
  margin-bottom: 40px;
  margin-left: 20px;
  font-family: 'Handlee', cursive;
}

#section-about p {
    display: inline;
  text-align: center;
  font-size: 20px;
  font-weight: 300;
  margin-left: 20px;
  letter-spacing: 2px;
}

.resume {
  padding-top: 100px;
  margin: 0 auto;
}


/************************ PORTFOLIO *********************/

#section-portfolio {
  background: #ced6e0;
  background-attachment: fixed;
  font-family: 'Handlee', cursive;

}


#section-portfolio img {
  height: 200px;
  display: block;
  margin: auto;
}

#section-portfolio h3 {
  text-align: center;  
  text-decoration: underline;
  margin-bottom: 40px;
  margin-top: 50px;
  padding-left: 40px;
}


#section-portfolio .portfolio-piece {
  border: 1px solid white;
  display: block;
  width: 250px;
  background-color: white;
  margin-top: 20px;
  margin-bottom: 25px;
  margin-left: auto ;
  margin-right: auto ;
  padding-bottom: 10px;
  border-radius: 5px;
  -webkit-box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
          box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
  max-width: 90%;
}



/************************* CONTACT **************************/

#section-contact p {
  font-size: 14px;
  padding-left: 40px;
  padding-top: 20px;
  word-wrap: break-word;
}

#section-contact .social-media-buttons > li {
  padding: 0px;
  text-align: center;
  display: inline;
  margin-left: 10px;
  margin-right: 10px;

}

#section-contact ul {
  margin-bottom: 20px;
  margin-top: 20px;
}

#section-contact p i {
  font-size: 18px;
  color: white;
  }

#section-contact li i {
  font-size: 40px;
  color: white;
}

#section-contact p a {
  color: black;
  padding-bottom: -2px;
  margin-top: 15px;
  color: white;
}

#section-contact p span {
  font-size: 18px;
  margin-top: 10px;
}



footer {
  text-align: center;
  font-size: 10px;
  color: white;
}