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

body {
  font-size: 30px;
  width: 100dvw;
  height: 100dvh;
  padding: 2em;
  background: linear-gradient(30deg, lightpink, pink, white);
  background-repeat: no-repeat;
  display: flex;
  justify-content: center;
  align-items: center;
}

.atom {
  height: 10em;
  width: 10em;
  position: relative;
  animation: spin 15s linear infinite alternate-reverse;
}

.nucleus {
  height: 5em;
  width: 5em;
  position: absolute;
  top: 3em;
  left: 3em;
}

.half_atom {
  display: flex;
}

.half_atom_2 {
  display: flex;
  margin-top: -0.6em;
}

.down {
  margin-left: -0.6em;
}

.particle {
  border-radius: 50%;
  height: 2em;
  width: 2em;
  box-shadow: 0 0 0.5em 0.1em whitesmoke;
}

.neutron {
  background-color: blue;
  box-shadow: 0 0 0.2em 0.1em powderblue;
}

.proton {
  background-color: red;
  box-shadow: 0 0 0.2em 0.1em pink;
}

.orbit {
  height: 12em;
  width: 10em;
  border-radius: 50%;
  border-left: 0.1em solid rgba(250, 250, 250, 0.3);
  border-right: 0.1em solid rgba(250, 250, 250, 0.3);
  position: absolute;
  top: 0;
  left: 0;
  animation: revolve 5s linear infinite;
}

.orbit::after {
  content: "";
  display: block;
  height: 1.2em;
  width: 1.2em;
  background-color: yellow;
  box-shadow: 0 0 1em 0.5em powderblue;
  border: 0.1em solid whitesmoke;
  border-radius: 50%;
  position: absolute;
}

.left.orbit::after {
  top: 1em;
  left: 1em;
  animation: grow-shrink 5s linear infinite;
}

.right.orbit {
  height: 10em;
  width: 12em;
}

.right.orbit::after {
  bottom: 1em;
  right: 1em;
  animation: grow-shrink 5s linear infinite reverse;
}

/* animations */

@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}

@keyframes revolve {
  50% {
    transform: rotate(180deg) scale(0.75);
  }

  to {
    transform: rotate(360deg) scale(1);
  }
}

@keyframes grow-shrink {
  50% {
    transform: scale(0.75);
    box-shadow: 0 0 0.5em 0.1em whitesmoke;
  }

  to {
    transform: scale(1);
    box-shadow: 0 0 1em 0.5em powderblue;
  }
}

h1 {
  position: absolute;
  font-family: cursive;
  font-size: 32px;
  top: 120px;
}