// ------- Scroll to top button
.btn-scroll-up {
  position: fixed;
  cursor: pointer;
  right: 3%;
  bottom: 1em;
  z-index: 2;
  // width: 2.6em;
  // height: 2.6em;
  opacity: 0;
  // background-color: $color-trans-red;
  // border-radius: 3px;
  @include transition(opacity 0.3s ease-out);

  color: $color-yellow-light;
  font-size: 2.7em;

  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display:  flex;
  -webkit-box-pack: center;
  -webkit-justify-content: center;
  -ms-flex-pack: center;
  justify-content: center;
  -webkit-box-align: center;
  -webkit-align-items: center;
  -ms-flex-align: center;
  align-items: center;

  // & > .fa {
  //   color: $color-yellow-light;
  //   font-size: 1.6em;
  //   text-shadow: none;
  //   margin-left: 0.1em;
  //   @include transform(rotate(-90deg));
  // }
}

// ------- Scroll to top button
.btn-scroll-up {
  position: fixed;
  cursor: pointer;
  right: 3%;
  bottom: 1em;
  z-index: 2;
  opacity: 0;
  @include transition(opacity 0.3s ease-out);

  color: $color-yellow-light;
  font-size: 3em;

  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display:  flex;
  -webkit-box-pack: center;
  -webkit-justify-content: center;
  -ms-flex-pack: center;
  justify-content: center;
  -webkit-box-align: center;
  -webkit-align-items: center;
  -ms-flex-align: center;
  align-items: center;
}

Enlarge scroll-top button, remove old SCSS
Enlarge scroll-top button, remove old SCSS
