style.css

@import url("https://fonts.googleapis.com/css2?family=Trispace:wght@300;400;700&display=swap");

* {
  margin: 0;
  font-family: "Trispace", sans-serif;
}

#toolbox {
  position: absolute;
  top: 8px;
  left: 8px;
  background-color: rgba(0, 0, 0, 0.5);
  border: 1px groove rgba(255, 255, 255, 0.5);
  color: white;
  padding: 12px;
  width: 400px;
  height: 80vh;
  display: block;
  overflow: auto;
}
.box {
  display: flex;
  justify-content: space-between;
}
.list {
  display: flex;
  flex-direction: column;
}

#btn {
  position: absolute;
  top: 8px;
  left: 8px;
  padding: 8px 24px;
  background-color: rgba(0, 0, 0, 0.5);
  border: 1px groove rgba(255, 255, 255, 0.5);
  color: white;
  cursor: pointer;
}

#btn:hover {
  background-color: rgba(255, 255, 255, 0.5);
}

#close {
  position: absolute;
  right: 10px;
  background-color: white;
}

#close:hover {
  background-color: rgba(255, 255, 255, 0.5);
  cursor: pointer;
}

.hidden {
  visibility: hidden;
  display: none;
}

header {
  margin-top: 40px;
  text-align: center;
  margin-bottom: 20px;
}

header h1 {
  margin-bottom: 6px;
}

header h4 {
  font-weight: 400;
}

.btn-planet {
  background-color: rgba(0, 0, 0, 0.5);
  text-align: center;
  width: 100%;
  margin-bottom: 15px;
  padding: 10px;
  border: 1px groove rgba(255, 255, 255, 0.5);
  box-sizing: border-box;
  cursor: pointer;
  color: white;
  display: block;
}

a.btn-planet {
  text-decoration: none;
  font-size: 13px;
}

.btn-planet:hover {
  background-color: rgba(255, 255, 255, 0.5);
  cursor: pointer;
}

.btn-back {
  position: absolute;
  top: 10px;
  left: 10px;
}

.btn-back:hover {
  background-color: rgba(255, 255, 255, 0.5);
  cursor: pointer;
}

div.page img {
  width: 100%;
  margin-bottom: 20px;
}

div.page p {
  text-align: center;
  margin-bottom: 20px;
}

#splash {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: black;
  width: 100vw;
  height: 100vh;
  color: white;
  display: flex;
  justify-content: center;
  align-items: center;
}
#splash div {
  text-align: center;
  animation: zoom-in;
  animation-duration: 5s;
}

@keyframes zoom-in {
  0% {
    transform: scale(0.8);
  }
  100% {
    transform: scale(1);
  }
}

#splash h1 {
  font-size: 100px;
}
#splash h2 {
  font-size: 50px;
  margin-bottom: 10px;
}
#splash p {
  color: rgba(255, 255, 255, 0.5);
}
#splash p#tips {
  margin-bottom: 25px;
  font-size: 10px;
  position: absolute;
  color: rgba(255, 255, 255, 0.2);
  bottom: 0;
  font-weight: 200;
  animation: blink;
  animation-duration: 1s;
  animation-iteration-count: infinite;
}

@keyframes blink {
  0% {
    opacity: 0;
  }
  50% {
    opacity: s;
  }
  100% {
    opacity: 1;
  }
}