.outer {
  position: fixed;
  left: 0;
  top: 0;
  right: 0;
  bottom: 0;
  width: 100vw;
  height: 100vh;
  overflow: hidden;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-align: center;
  -ms-flex-align: center;
  align-items: center;
  -webkit-box-pack: center;
  -ms-flex-pack: center;
  justify-content: center;
  font-family: sans-serif;
}
.inner {
  padding: 15px;
  text-align: center;
  max-width: 400px;
}
h1 {
  font-size: 1em;
}
a,
button {
  border: none;
  -webkit-appearance: none;
  -moz-appearance: none;
  appearance: none;
  background: rgba(0, 0, 0, 0.05);
  font-size: clamp(10px, 7vw, 30px);
  margin: 2px;
  border-radius: 2px;
  font-weight: 700;
}
a.submit,
button.submit {
  background: #6378f6;
  color: #fff;
}
a.backspace,
button.backspace {
  color: rgba(0, 0, 0, 0.5);
}
input {
  width: 100%;
  line-height: 50px;
  font-size: 30px;
  border: 1px solid rgba(0, 0, 0, 0.1);
  height: 50px;
  text-align: center;
}
.keypad .row {
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
}
.keypad a,
.keypad button {
  height: 100%;
  width: 100%;
  padding: 15px 0;
  text-align: center;
}
.keypad a:disabled,
.keypad button:disabled {
  opacity: 0.3;
  background: rgba(0, 0, 0, 0.05) !important;
  color: inherit !important;
}