/* Celkový overlay */
#start-overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100vw;
  height: 100vh;
  background: rgba(255, 255, 255, 0.05);
  backdrop-filter: blur(14px) saturate(160%);
  -webkit-backdrop-filter: blur(14px) saturate(160%);
  z-index: 9999;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
  animation: fadeInOverlay 1.2s ease forwards;
  opacity: 0;
}

/* Jemné světelné tečky v pozadí */
#start-overlay::before,
#start-overlay::after {
  content: '';
  position: absolute;
  width: 100%;
  height: 100%;
  background-image: radial-gradient(circle at 20% 30%, rgba(63, 224, 190, 0.2) 0%, transparent 70%),
                    radial-gradient(circle at 80% 70%, rgba(41, 201, 160, 0.15) 0%, transparent 80%);
  background-repeat: no-repeat;
  animation: floatGlow 20s ease-in-out infinite;
  z-index: -1;
}

#start-overlay button {
  padding: 20px 60px;
  font-size: 1.4rem;
  font-weight: bold;
  background: linear-gradient(135deg, #3FE0BE, #29c9a0);
  color: white;
  border: none;
  border-radius: 50px;
  box-shadow: 0 12px 35px rgba(63, 224, 190, 0.35), inset 0 0 10px rgba(255, 255, 255, 0.1);
  cursor: pointer;
  transition: all 0.4s ease;
  letter-spacing: 1.5px;
  text-transform: uppercase;
  animation: slideUp 1.2s ease forwards 0.5s;
  opacity: 0;
  backdrop-filter: blur(4px);
}

/* Hover efekt */
#start-overlay button:hover {
  transform: scale(1.07);
  background: linear-gradient(135deg, #2ec9a4, #1ca98a);
  box-shadow: 0 15px 40px rgba(63, 224, 190, 0.55), inset 0 0 12px rgba(255, 255, 255, 0.12);
}

/* Přechod overlay */
@keyframes fadeInOverlay {
  from {
    opacity: 0;
    transform: scale(1.02);
  }
  to {
    opacity: 1;
    transform: scale(1);
  }
}

/* Slide-up efekt tlačítka */
@keyframes slideUp {
  from {
    opacity: 0;
    transform: translateY(40px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* Pohyb světelných efektů */
@keyframes floatGlow {
  0%, 100% {
    background-position: 20% 30%, 80% 70%;
  }
  50% {
    background-position: 25% 35%, 75% 65%;
  }
}