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

body {
  background-color: #000;
  font-family: monospace;
}

a {
  color: #000;
  text-decoration: none;
  position: relative;
}

a::before {
  content: "";
  position: absolute;
  width: 100%;
  height: 4px;
  border-radius: 4px;
  background: linear-gradient(
    to right,
    #000 40%,
    rgb(255, 255, 255, 0) 40% 60%,
    #000 60%
  );
  bottom: 5px;
  left: 0;
  transform-origin: left;
  transform: scaleX(1);
  transition: transform 0.3s ease-in-out;
}

a:hover::before {
  transform-origin: right;
  transform: scaleX(0);
}

/* Calculator */
#calculator {
  border: solid 1.5px #fff;
  border-radius: 10px;
  background-color: #6c757d;
  width: 300px;
  height: 400px;
  padding: 35px 30px 40px 30px;
  position: absolute;
  top: 25px;
  left: 50%;
  transform: translateX(-50%);
  text-align: center;
}

#calculation-area {
  background-color: #fff;
  height: 100px;
  opacity: 95%;
  border-radius: 5px;
  margin-left: 5px;
  margin-bottom: 20px;
  padding: 12.5px;
  text-align: right;
}

#topCalcDisp {
  color: #6c757d;
  font-size: 25px;
  overflow: scroll;
}

#bottomCalcDisp {
  color: #000;
  font-size: 40px;
  overflow: scroll;
}

.scale-animation {
  animation-name: scale1;
  animation-duration: 0.1s;
  animation-iteration-count: 1;
}

.btn-rows button {
  background-color: #000;
  color: #fff;
  width: 45px;
  height: 35px;
  border: none;
  border-radius: 5px;
  font-family: monospace;
  font-size: 18px;
  margin-left: 5px;
  margin-bottom: 10px;
}

.btn-num:active,
.btn-decimal:active,
.btn-click-anim {
  animation-name: btn-click;
  animation-duration: 0.1s;
  animation-iteration-count: 1;
}

.btn-rows .btn-optr {
  background-color: #f0c107;
}

.btn-rows .btn-del {
  background-color: #dc3545;
}

.btn-rows .btn-big {
  width: 102.5px;
}

.btn-rows .btn-output {
  background-color: #198754;
}

.btn-rows button:hover {
  cursor: pointer;
}

/* Math Constants Dropdown */
#mathConstantsDropdown {
  color: #fff;
  font-size: 20px;
  max-width: 200px;
  padding-bottom: 0.1px;
  position: relative;
  left: 50%;
  transform: translateX(-50%);
}

#mathConstantsDropdown summary {
  color: #000;
  text-align: center;
  width: 200px;
  border-radius: 8px;
  margin-bottom: 25px;
  box-shadow: 0 0 40px 10px #fff, 0 0 100px 0 #fff inset;
  -moz-box-shadow: 0 0 40px 10px #fff, 0 0 100px 0 #fff inset;
  -webkit-box-shadow: 0 0 40px 10px #fff, 0 0 100px 0 #fff inset;
  -ms-box-shadow: 0 0 40px 10px #fff, 0 0 100px 0 #fff inset;
  -o-box-shadow: 0 0 40px 10px #fff, 0 0 100px 0 #fff inset;
}

#mathConstantsDropdown summary:hover {
  cursor: pointer;
}

#mathConstantsDropdown li {
  font-size: 15px;
  text-align: left;
  list-style-type: none;
  margin-bottom: 10px;
}

#mathConstantsDropdown > div {
  position: relative;
  top: 10px;
  padding-bottom: 25px;
}

#mathConstantsDropdown li:first-child {
  margin-top: -40px;
}

@keyframes scale1 {
  100% {
    transform: scale(1.1);
  }
}

@keyframes btn-click {
  100% {
    transform: scale(1.1);
    box-shadow: 0 0 5px 5px #f0f0f0;
  }
}