Why are my Font Awesome fonts and text blurry?

.lblBiancoMenu {
  color: white !important;
}

.subCat .li {
  color: white;
}

.parent {
  width: 100%;
  height: 30px;
  border: 1px solid #AAA;
  white-space: nowrap;
  overflow-y: hidden;
}

.child {
  height: 45px;
  overflow-x: auto;
}

.redBack {
  background-color: firebrick;
  /* text-shadow: 1px 1px 1px #ccc; *******************************/
  font-size: 1.0em;
  color: white !important;
}

#header-content {
  position: absolute;
  bottom: 0;
  left: 0;
}

.flex-contianer {
  display: flex;
  justify-content: space-between;
  background-color: firebrick;
}

.left-btn {
  width: 100px;
}

.right-btn {
  width: 100px;
}

.btn {
  width: 25%;
}

<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.7.0/css/all.css" integrity="sha384-lZN37f5QGtY3VHgisS14W3ExzMWZxybE1SJSEsQp9S+oqd12jhcu+A56Ebc1zFSJ" crossorigin="anonymous">

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" />

<div id="header-content" style="width:100%" class="btn-group  btn-group-toggle " data-toggle="buttons">

  <label class="btn btn-secondary redBack"><i class="fas fa-home"></i><br />
                        <input type="radio" name="options1" id="option1" checked onclick="window.location.href='Index.aspx';">Home
                      </label>
  <label class="btn btn-secondary  redBack"><i class="fa fa-book-open"></i><br />
                        <input type="radio" name="options2" id="option2" >Menù
                      </label>
  <label class="btn btn-secondary redBack"><i class="fa fa-shopping-cart"></i><br />
                        <input type="radio" name="options3" id="option3" onclick="window.location.href='Carrello.aspx';">Carrello
                      </label>
  <label class="btn btn-secondary redBack"><i class="far fa-address-card"></i><br />
                        <a href="registrazione.aspx"><input type="radio" name="options4" id="option4">Account</a>
                      </label>
</div>