:root {
  --card-bg: #12131a;            /* Flat slate dark background */
  --text-color: #00f5ff;         /* Cyber Neon Cyan */
  --label-color: #ffd700;        /* Gold label */
  --card-radius: 16px;           /* Rounded corner radius for mobile scale */
}

/* Mobile-optimized full width wrapper */
.countdown-clock-wrapper {
  width: 100%;
  max-width: 480px;              /* Locked to phone sizing constraints */
  margin: 1.5rem auto;
  padding: 0 0.75rem;
}

/* 2x2 grid is standard and fits naturally on mobile portrait displays */
.flip-clock {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 20px 16px;
  width: 100%;
}

.unit-box {
  display: flex;
  flex-direction: column;
  align-items: center;
  background: rgba(255, 255, 255, 0.02);
  padding: 15px 10px;
  border-radius: var(--card-radius);
  border: 1px solid rgba(255, 255, 255, 0.03);
}

.unit-label {
  margin-top: 12px;
  color: var(--fc-label-color, var(--label-color));
  font-size: 0.95rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  font-weight: 700;
}

/* --- Clean Full-Card Rigging --- */
.flip-card {
  position: relative;
  width: 100%;
  height: 110px;                 /* Ideal height footprint for mobile viewports */
  perspective: 1000px;           /* Depth environment for whole card tumble */
  transform-style: preserve-3d;
}

.card-face {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  display: grid;
  place-items: center;
  font-size: 4rem;               /* Big, highly scannable numbers */
  font-weight: 800;
  color: var(--text-color);
  background: var(--card-bg);
  border-radius: var(--card-radius);
  border: 1px solid rgba(255, 255, 255, 0.05);
  box-shadow: 0 10px 20px rgba(0, 0, 0, 0.5);
  backface-visibility: hidden;   /* Keeps flipped-away side invisible */
  will-change: transform;         /* Offloads execution workloads to system GPU */
  transition: transform 0.5s cubic-bezier(0.4, 0, 0.2, 1), 
              border-color 0.5s, 
              box-shadow 0.5s;
}

/* Position tracking configuration layers */
.current-val {
  z-index: 2;
  transform: rotateX(0deg);
}

.next-val {
  z-index: 1;
  transform: rotateX(-180deg);   /* Hidden behind, upside down waiting to turn */
}

/* --- Trigger States Driven by Javascript --- */
.flip-card.animate .current-val {
  transform: rotateX(180deg);
}

.flip-card.animate .next-val {
  transform: rotateX(0deg);
  z-index: 3;
  /* Glow flash burst effect on completion */
  border-color: var(--text-color);
  box-shadow: 0 0 15px rgba(0, 245, 255, 0.4), 0 10px 20px rgba(0, 0, 0, 0.5);
}

/* --- Desktop Scaling Adjustments (Keeps layout clean if viewed on PC) --- */
@media (min-width: 580px) {
  .countdown-clock-wrapper {
    max-width: 800px;
  }
  .flip-clock {
    grid-template-columns: repeat(4, 1fr); /* Snaps back to straight inline row */
  }
  .flip-card {
    height: 140px;
  }
  .card-face {
    font-size: 5rem;
  }
}