* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  height: 100%;
}

body {
  font-family: sans-serif;
  background: linear-gradient(#141e30, #243b55);
}

.calc-box {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 400px;
  padding: 40px;
  transform: translate(-50%, -50%);
  background: rgba(0, 0, 0, 0.5);
  box-sizing: border-box;
  box-shadow: 0 15px 25px rgba(0, 0, 0, 0.6);
  border-radius: 60px;
}

.display {
  display: inline-block;
  position: relative;

  background-color: #141e30;
  width: 100%;
  height: 6.5vh;
  padding: 10px 20px;
  border-radius: 10px;

  color: #03e9f4;
  line-height: 2.5vh;
  letter-spacing: 2px;
  text-align: right;

  overflow: hidden;
  transition: 0.5s;
}

.display h1,
.display h4 {
  color: #03e9f4;
}

.calc {
  overflow: hidden;
  display: grid;
  grid-template-columns: 1fr 1fr 1fr 1fr;
  grid-template-areas:
    'A1 B1 C1 D'
    'A2 B2 C2 D'
    'A3 B3 C3 D'
    'A4 B4 C4 D';
  user-select: none;
}

.calc div {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;

  background-color: #141e30;
  border: #243b5580 1px solid;
  color: #ffffff;
}

.calc .right {
  grid-area: D;
}

.calc div:hover {
  box-shadow: inset 0 0 5px #03e9f4;
}

.right > div {
  background-color: #243b55;
  border: #141e30 1px solid;
  border-right: none;
  border-left: none;

  width: 100%;

  color: #ffffff;
  padding: 20px;
}

.display:hover {
  transform: scale(1.05);
  background-color: #243b55;
}

.calc-box .display span {
  position: absolute;
  display: block;
}

.display span:nth-child(1) {
  top: 0;
  left: -100%;
  width: 100%;
  height: 2px;
  background: linear-gradient(90deg, transparent, #03e9f4);
  animation: btn-anim1 1s linear infinite;
}

@keyframes btn-anim1 {
  0% {
    left: -100%;
  }

  50%,
  100% {
    left: 100%;
  }
}

.display span:nth-child(2) {
  top: -100%;
  right: 0;
  width: 4px;
  height: 100%;
  background: linear-gradient(180deg, transparent, #03e9f4);
  animation: btn-anim2 1s linear infinite;
  animation-delay: 0.25s;
}

@keyframes btn-anim2 {
  0% {
    top: -100%;
  }

  50%,
  100% {
    top: 100%;
  }
}

.display span:nth-child(3) {
  bottom: 0;
  right: -100%;
  width: 100%;
  height: 6px;
  background: linear-gradient(270deg, transparent, #03e9f4);
  animation: btn-anim3 1s linear infinite;
  animation-delay: 0.5s;
}

@keyframes btn-anim3 {
  0% {
    right: -100%;
  }

  50%,
  100% {
    right: 100%;
  }
}

.display span:nth-child(4) {
  bottom: -100%;
  left: 0;
  width: 4px;
  height: 100%;
  background: linear-gradient(360deg, transparent, #03e9f4);
  animation: btn-anim4 1s 0.75s linear infinite;
  /* animation-delay:  */
}

@keyframes btn-anim4 {
  0% {
    bottom: -100%;
  }

  50%,
  100% {
    bottom: 100%;
  }
}