body{
  background-color: rgb(41, 41, 41);
}
.login_box{
  position: absolute;
  top: 50%;
  left: 50%;
  width: 400px;
  padding: 40px;
  transform: translate(-50%,-50%);
  background: rgba(24, 20, 20, 0.987);
  box-sizing: border-box;
  box-shadow: 0 15px 25px rgba(0, 0, 0, 0.6);
  border-radius: 10px;
}

.login_box .user_box{
  position: relative;
}

.login_box .user_box input{
  width: 100%;
  padding: 10px 0;
  font-size: 16px;
  color: #fff;
  margin-bottom: 30px;
  border: none;
  border-bottom: 1px solid #fff;
  outline: none;
  background: transparent;
}

.login_box .user_box label{
  position: absolute;
  top: 0;
  left: 0;
  padding: 10px 0;
  font-size: 16px;
  color: #fff;
  pointer-events: none;
  transition: 0.5s;
}

.login_box .user_box input:focus ~ label,
.login_box .user_box input:valid ~ label{
  top: -20px;
  left: 0;
  color: #bdb9b9;
  font-size: 12px;
}

.login_box form a{
  position: relative;
  display: inline-block;
  padding: 10px 20px;
  color: #ffffff;
  font-size: 16px;
  text-decoration: none;
  text-transform: uppercase;
  overflow: hidden;
  transition: 0.5s;
  margin-top: 40px;
  letter-spacing: 4px;
}

.login_box a:hover{
  background: #03f40f;
  border-radius: 5px;
  box-shadow: 0 0 5px #03f40f,
              0 0 25px #03f40f,
              0 0 50px #03f40f,
              0 0 100px #03f40f;               
}

.login_box a span{
  position: absolute;
  display: block;
}

.login_box a span:nth-child(1){
  bottom: 2px;
  left: -100%;
  width: 100%;
  height: 2px;
  background: linear-gradient(90deg, transparent, #03f40f);
  animation: animate 2s linear infinite;
}

@keyframes animate{
  0%{
    left: -100%;
  }
  50%,100%{
    left: 100%;
  }
}