/* =========================================================
   DEPARTURE BOARD / 3D FLAPS
========================================================= */

/* =========================================================
   DEPARTURE BOARD / 3D FLAPS — SKY / GLASS STYLE
========================================================= */
.header {

  background: linear-gradient(
    180deg,
    #dbe7fb 0%,
    #c6d7f2 50%,
    #b1c7e6 100%
  );

  box-shadow:
    inset 0 -1px 0 rgba(255,255,255,0.6),
    0 10px 30px rgba(80,120,180,0.35);

}
.letter {
  position: relative;
  display: inline-block;

  font-family: "JetBrains Mono", monospace;
  font-weight: 600;
  letter-spacing: 0.12em;

  color: #1e3a5f;
  background: transparent;

  text-shadow:
    0 1px 0 rgba(255,255,255,0.7),
    0 3px 10px rgba(90,140,200,0.4);
}

/* One character cell */
.flap {
  width: 4vw;
  height: 4vw;
  position: absolute;
  top: 0;

  perspective: 900px;

  border-radius: 0.4rem;
  overflow: hidden;

  background: rgba(255,255,255,0.65);

  box-shadow:
    inset 0 0 0 1px rgba(255,255,255,0.9),
    0 4px 10px rgba(90,130,190,0.35);
}

/* Upper / lower halves */
.half {
  width: 100%;
  height: 2vw;
  position: absolute;
  overflow: hidden;

  background: linear-gradient(
    180deg,
    #eef4ff 0%,
    #d6e2f5 100%
  );

  transform-style: preserve-3d;

  animation-timing-function: ease-in;
  animation-duration: 0.28s;
  animation-iteration-count: infinite;
}

/* Faster convergence */
.fast .half {
  animation-duration: 0.14s;
}

/* Divider (mechanical seam) */
.divider {
  position: absolute;
  top: 2vw;
  left: 0;
  right: 0;
  height: 2px;

  background: linear-gradient(
    90deg,
    transparent,
    rgba(0,0,0,0.35),
    transparent
  );

  box-shadow:
    0 1px 2px rgba(0,0,0,0.25);

  z-index: 2;
  opacity: 1;
  transition: opacity 0.1s ease;
}

/* Panel positioning */
.prev {
  top: 2vw;
}

.back,
.front {
  backface-visibility: hidden;
  transform: translateZ(1px);
}

.front {
  transform-origin: center bottom;
}

.back {
  top: 2vw;
  transform-origin: center top;
}

/* Letter vertical offsets */
.front .letter,
.next .letter {
  top: -0.45vw;
}

.back .letter,
.prev .letter {
  top: -2.45vw;
}

/* =========================================================
   ACTIVE FLIP STYLING
========================================================= */

.animated .front {
  animation-name: flipFront;
  box-shadow:
    inset 0 -6px 10px rgba(90,130,190,0.45);
}

.animated .back {
  animation-name: flipBack;
  box-shadow:
    inset 0 6px 10px rgba(90,130,190,0.45);
}

/* =========================================================
   KEYFRAMES — softened sky tones
========================================================= */

@keyframes flipFront {
  0% {
    transform: rotateX(0deg);
    background-color: #eef4ff;
  }
  100% {
    transform: rotateX(180deg);
    background-color: #cfdcf2;
  }
}

@keyframes flipBack {
  0% {
    transform: rotateX(180deg);
    background-color: #d6e2f5;
  }
  100% {
    transform: rotateX(0deg);
    background-color: #eef4ff;
  }
}






















/* /* =========================================================
   GLOBAL STYLES
========================================================= * /


body {
  font-family: "Segoe UI", system-ui, sans-serif;
  background: #111;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1.2rem;
  padding: 2rem;
}

.controls button {
  background: #333;
  color: #fff;
  border: none;
  padding: 0.4rem 0.8rem;
  cursor: pointer;
  border-radius: 4px;
}

/* Board container * /
.board {
  padding: 1rem 1.2rem;
  border-radius: 6px;
  box-shadow: inset 0 -3px 0 rgba(0,0,0,0.4);
}

/* Rows * /
.row {
  display: flex;
  gap: 0.35rem;
}

/* Individual cells * /
.cell {
  width: 42px;
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.8rem;
  font-weight: 600;
  border-radius: 4px;
  box-shadow:
    inset 0 1px 0 rgba(255,255,255,0.05),
    inset 0 -2px 0 rgba(0,0,0,0.5);
}

/* =========================================================
   DEPARTURE BOARD / 3D FLAPS
========================================================= * /
.flap {
  width: 4vw;
  height: 4vw;
  position: absolute;
  top: 0;
  perspective: 800px;
}

.half {
  width: 100%;
  height: 2vw;
  position: absolute;
  overflow: hidden;
  transform-style: preserve-3d;
  animation-timing-function: ease-in;
  animation-duration: 0.28s;
  animation-iteration-count: infinite;
  background-color: #444;
}

.fast .half {
  animation-duration: 0.14s;
}

.divider {
  position: absolute;
  top: 2vw;
  left: 0;
  right: 0;
  height: 2px;
  background-color: #111;
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.6);
  z-index: 2;
  opacity: 1;
  transition: opacity 0.1s ease;
}

.prev {
  top: 2vw;
}
.back,
.front {
  backface-visibility: hidden;
  transform: translateZ(1px);
}

.front {
  transform-origin: center bottom;
}
.back {
  top: 2vw;
  transform-origin: center top;
}

/* Letter alignment * /
.front .letter,
.next .letter {
  top: -0.5vw;
}
.back .letter,
.prev .letter {
  top: -2.5vw;
}

/* Flip animation * /
.animated .front {
  animation-name: flipFront;
  box-shadow: inset 0 -6px 8px rgba(0, 0, 0, 0.4);
}
.animated .back {
  animation-name: flipBack;
  box-shadow: inset 0 6px 8px rgba(0, 0, 0, 0.4);
}

@keyframes flipFront {
  0% {
    transform: rotateX(0deg);
    background-color: #444;
  }
  100% {
    transform: rotateX(180deg);
    background-color: #1c1c1c;
  }
}
@keyframes flipBack {
  0% {
    transform: rotateX(180deg);
    background-color: #222;
  }
  100% {
    transform: rotateX(0deg);
    background-color: #444;
  }
}

/* =========================================================
   BOARD STYLES / THEMES
========================================================= * /

/* --- Classic Airport --- * /
.board.classic {
  background: #1e1f22;
}
.board.classic .cell {
  background: #2b2d31;
  color: #f5f5f2;
  text-shadow: 0 1px 0 rgba(0,0,0,0.5);
}

/* --- Modern Light --- * /
.board.light {
  background: #f4f6f8;
}
.board.light .cell {
  background: #e1e5ea;
  color: #1a1a1a;
  box-shadow:
    inset 0 1px 0 rgba(255,255,255,0.6),
    inset 0 -2px 0 rgba(0,0,0,0.15);
}

/* --- Night Airport --- * /
.board.night {
  background: #0b1220;
}
.board.night .cell {
  background: #111827;
  color: #e5e7eb;
  text-shadow: 0 1px 0 rgba(0,0,0,0.6);
}

/* =========================================================
   STYLE TEST COLORS
========================================================= * /
.board.test1 { background: #001f3f; }      /* deep navy * /
.board.test1 .cell { background: #003366; color: #33ccff; }

.board.test2 { background: #1a001a; }      /* dark purple * /
.board.test2 .cell { background: #330033; color: #ff99ff; }

.board.test3 { background: #001a00; }      /* forest green * /
.board.test3 .cell { background: #003300; color: #99ff99; }

.board.test4 { background: #220000; }      /* deep red * /
.board.test4 .cell { background: #440000; color: #ff6666; } */