@import url('https://fonts.googleapis.com/css?family=Orbitron');

body {
  background-color: #f7f7f7;
  color: #000;
  font-size: 16px;
  font-family: 'Orbitron', sans-serif;
  margin: 0;
}

@media screen and (max-width: 400px) {
  /* For mobile phones: */
  html {
    font-size: 12px;
  }
}

.container {
  font-family: 'Orbitron', sans-serif;
  font-weight: bold;
  background-color: #0e0e0e;
  margin: 0 auto;
  margin-top: 1rem;
  padding: .3rem;
  max-width: 22rem;
  border: .2rem solid #e1e1e1;
  border-radius: 1.2rem;
  box-shadow: .1rem .1rem .5rem .2rem #3d3d3d;
}

@media screen and (max-width: 600px) {
  /* For mobile phones: */
  .container {
    margin: 0 auto;
    margin-top: .5rem;
    max-width: 100%;
  }
}

#screen-top {
  display: flex;
  justify-content: flex-end;
  align-items: top;
  font-size: 1.2rem;
  word-break: break-all;
  text-align: right;
  min-height: 3rem;
  padding: .1rem;
  padding-top: .5rem;
  padding-right: 1rem;
  background-color: #1a1a1a;
  color: #fff;
  border: 1px solid #0e0e0e;
  border-top-left-radius: .6rem;
  border-top-right-radius: .6rem;
}

#screen-bottom {
  display: flex;
  justify-content: flex-end;
  align-items: center;
  font-size: 1.4rem;
  text-align: right;
  background-color: #1a1a1a;
  color: #fff;
  padding-right: .8rem;
  height: 2.2rem;
  border: 1px solid #0e0e0e;
}

.keyboard {
  display: grid;
  grid-template-columns: 25% 25% 25% 25%;
  grid-template-rows: auto;
  height: 15rem;
  background-color: #1a1a1a;
}

button {
  font-family: 'Orbitron', sans-serif;
  font-size: 1.2rem;
  font-weight: bold;
  background-color: #1a1a1a;
  color: #fff;
  outline: none;
  border: 2px solid #0e0e0e;
  position: relative;
  appearance: none;
  cursor: pointer;
  overflow: hidden;
}

button span {
  position: relative;
  pointer-events: none;
}

button:active {
  outline: .1rem solid #888;
  outline-offset: -2px;
}

button::before {
  --size: 0;
  content: '';
  position: absolute;
  left: var(--x);
  top: var(--y);
  width: var(--size);
  height: var(--size);
  background: radial-gradient(circle closest-side, #7a7a7a, transparent);
  transform: translate(-50%, -50%);
  transition: width .2s ease, height .2s ease;
}

.operator::before {
  background: radial-gradient(circle closest-side, #2197ff, transparent);
}

#backspace::before, #clear-entry::before, #clear::before {
  background: radial-gradient(circle closest-side, #ff2020, transparent);
}

#switch::before {
  background: radial-gradient(circle closest-side, #ff9011, transparent);
}

#equal::before {
  background: radial-gradient(circle closest-side, #60ff73, transparent);
}

button:hover::before {
  --size: 300px;
}

.keyboard>.operator {
  background-color: #222;
  color: #fff;
}

.keyboard>.function {
  background-color: #222;
  color: #fff;
}

.keyboard>#switch {
  font-size: .8rem;
  border-bottom-left-radius: .6rem;
}

.keyboard>#equal {
  background-color: #fff;
  color: #000;
  border-bottom-right-radius: .6rem;
}

.footer {
  font-size: 0.9em;
  color: #303030;
  text-align: center;
  margin-top: 30px;
}
.footer>a {
  color: #007cff;
  font-weight: bold;
  text-decoration: none !important;
}