* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
body {
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-image: url('bg_2.jpg');
  background-size: cover;
}

main {
  padding: 10px 20px;
  height: 620px;
  width: 95%;
  left: 50%;
  top: 50%;
  position: absolute;
  transform: translate(-50%, -50%);
  border: 1px solid black;
  background-color: rgba(32,31,31,0.85);
  border-radius: 30px;
  box-sizing: border-box;
}

main h2 {
  font-family: Monospace;
  text-align: center;
  color: #8ff7ff;
  font-size: 20px;
}

main #run_btn {
  font-family: Courier;
  font-weight: 800;
  width: 80px;
  height: 60px;
  left: 50%;
  bottom: 10px;
  position: relative;
  transform: translateX(-50%);
  border-radius: 20px;
  outline: none;
  border: 1px solid;
  background-image: linear-gradient(#71f9ff, #00bfc6);
  font-size: 30px;
  color: #ffffff;
  font-weight: 700;
  cursor: pointer;
}

main #run_btn:focus{
  border-color: #00ccdc9d;
  transition: .4s;
}

main #run_btn:disabled{
  color: #f0efef;
  background-color: #4e4e4e;
}

.txt_field {
  position: relative;
  margin: 15px 0px;
  font-family: Consolas;
}

.txt_field #key{
  width: 100%;
  padding: 0px 5px;
  height: 40px;
  font-size: 16px;
  border: 1px solid rgba(255,255,255,0.78);
  border-radius: 30px;
  background: rgba(255,255,255,0.78);
  outline: none;
}

.txt_field textarea{
  width: 100%;
  padding: 5px;
  height: 300px;
  font-size: 16px;
  border: 1px solid rgba(255,255,255,0.78);
  border-radius: 15px;
  background: rgba(255,255,255,0.78);
  outline: none;
}

.txt_field textarea ~ label,
.txt_field #key ~ label{
  position: absolute;
  top: 50%;
  left: 5px;
  color: #adadad;
  transform: translateY(-50%);
  font-size: 16px;
  font-weight: 750;
  pointer-events: none;
  transition: .3s;
}

.txt_field textarea ~ label {
  top: 15px;
}

.txt_field #key:focus ~ label,
.txt_field textarea:focus ~ label,
.txt_field #key:valid ~ label,
.txt_field textarea:valid ~ label{
  top: -7px;
  font-size: 12px;
  color: #8ff7ff;
}

.txt_field #decrypt{
  width: 20px;
  margin: 10px;
  right: 0;
  height: 20px;
  border: 1px solid rgba(255,255,255,0.78);
  border-radius: 30px;
  background: rgba(255,255,255,0.78);
  outline: none;
}

.txt_field #decrypt ~ span {
  position: relative;
  top: -2px;
  left: -5px;
  color: #00ccdc9d;
  font-weight: 700;
  font-size: 18px;
  pointer-events: none;
  transition: .3s;
}