.btn,
a.btn,
button.btn {
  font-weight: 700;
  line-height: 1.5;
  position: relative;
  display: inline-block;
  padding: 10px 20px 10px 20px;
 margin: 10px 20px 10px 20px;
  cursor: pointer;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
  -webkit-transition: all 0.3s;
  transition: all 0.3s;
  text-align: center;
  vertical-align: middle;
  text-decoration: none;
  letter-spacing: 0.1em;
  color: #212529;
  border-radius: 0.5rem;
}




/*その他と主な共通部分は省略*/

a.btn-flat {
  overflow: hidden;

  color: #fff;
  border-radius: 0;
  background: #008000;
}

a.btn-flat span {
  position: relative;
  z-index: 1;
}

a.btn-flat:before {
  position: absolute;
  top: 0;
  left: calc(-100% + 10px);

  width: 100%;
  height: 100%;

  content: '';
  -webkit-transition: all .5s ease-in-out;
  transition: all .5s ease-in-out;
  -webkit-transform: translateX(0) translateY(0);
  transform: translateX(0) translateY(0);

  background: #9ac123;
}

a.btn-flat:after {
  position: absolute;
  top: 0;
  right: calc(-100% + 10px);

  width: 100%;
  height: 100%;

  content: '';
  -webkit-transition: all .5s ease-in-out;
  transition: all .5s ease-in-out;
  -webkit-transform: translateX(0) translateY(0);
  transform: translateX(0) translateY(0);

  background: #9ac123;
}

a.btn-flat:hover:before {
  -webkit-transform: translateX(50%) translateY(0);
  transform: translateX(50%) translateY(0);
}

a.btn-flat:hover:after {
  -webkit-transform: translateX(-50%) translateY(0);
  transform: translateX(-50%) translateY(0);
}



@media screen and (max-width: 650px){	
a.btn-flat {
    overflow: hidden;
    color: #fff;
    border-radius: 0;
    background: #008000;
    width: 85%;
    padding: 10px;
    margin: 10px;
}
}