html, body {
  margin: 0;
  height: 100vh;
  overflow: hidden;

  background: linear-gradient(-45deg, #0f172a, #1e293b, #0ea5e9, #22c55e);
  background-size: 400% 400%;
  animation: gradientShift 12s ease infinite;

  color: white;
  font-family: Arial;
}

#problem {
  position: absolute;
  top: 10%;
  left: 50%;
  transform: translateX(-50%);

  font-size: 76px;
  text-align: center;
}

#equation {
  position: absolute;
  top: 30%;
  left: 50%;
  transform: translateX(-50%);
  font-size: 32px;

  font-family: "Comic Sans MS", cursive; /* surprisingly effective */
  text-shadow: 
    0 0 2px rgba(255,255,255,0.8),
    0 0 6px rgba(255,255,255,0.4);
  transition: opacity 0.5s ease, transform 0.5s ease;
}

#explanation {
  position: absolute;
  top: 45%;
  left: 50%;
  transform: translateX(-50%);
  font-size: 24px;
  opacity: 0.8;
} 28px;

#steps {
  position: absolute;
  top: 27%;                 /* below the problem */
  left: 50%;
  transform: translateX(-50%);

  width: 800px;
  text-align: center;
  font-size: 28px;
}

#waveCanvas {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 0;
}

#particleCanvas {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 0;
}

.fade-out {
  opacity: 0;
  transform: translateX(-50%) scale(0.95);
}

.fade-in {
  opacity: 1;
  transform: translateX(-50%) scale(1);
}

.chalk-in {
  opacity: 0;
  transform: scale(1.05);
  filter: blur(6px);
}

.chalk-in-active {
  opacity: 1;
  transform: scale(1);
  filter: blur(0px);
  transition: all 0.4s ease;
}

@keyframes gradientShift {
  0% { background-position: 0% 50%; }
  50% { background-position: 100% 50%; }
  100% { background-position: 0% 50%; }
}