/* --- skills: card grid grouped by category --- */
.skills__groups {
  display: grid;
  gap: 3rem;
}

.skills__category {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--color-matcha);
  margin: 0 0 1.25rem;
  display: flex;
  align-items: center;
  gap: 1rem;
}

.skills__category::after {
  content: "";
  flex: 1;
  height: 1px;
  background: var(--color-line);
}

.skills__grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(170px, 1fr));
  gap: 0.75rem;
}

.skill-card {
  border: 1px solid var(--color-line);
  border-radius: var(--radius);
  padding: 1.1rem 1.25rem;
  background: var(--color-surface);
  position: relative;
  overflow: hidden;
  transform-style: preserve-3d;
  perspective: 1800px;
  transform: perspective(1800px) rotateX(var(--tilt-rx, 0deg)) rotateY(var(--tilt-ry, 0deg));
  transition: border-color 0.2s var(--ease-wa), transform 0.4s var(--ease-wa), background 0.2s var(--ease-wa), box-shadow 0.2s var(--ease-wa);
}

.skill-card.is-tilting {
  transition: border-color 0.2s var(--ease-wa), transform 0.08s ease-out, background 0.2s var(--ease-wa), box-shadow 0.2s var(--ease-wa);
}

.skill-card::after {
  content: "";
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: radial-gradient(
    circle 160px at var(--glow-x, 50%) var(--glow-y, 50%),
    color-mix(in srgb, var(--color-matcha-light) 15%, transparent),
    transparent 70%
  );
  opacity: var(--glow-opacity, 0);
  pointer-events: none;
  transition: opacity 0.3s ease;
  z-index: 1;
}

.skill-card::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: var(--color-matcha);
  opacity: 0;
  transition: opacity 0.2s ease;
  z-index: 2;
}

.skill-card:hover {
  border-color: var(--color-matcha);
  background: var(--color-surface-2);
  box-shadow: 0 8px 22px rgba(0, 0, 0, 0.28);
}

.skill-card:hover::before {
  opacity: 1;
}

.skill-card__name {
  font-family: var(--font-display);
  font-weight: 500;
  margin: 0;
  font-size: 0.95rem;
  color: var(--color-text);
  word-break: break-word;
}

.skill-card__level {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--color-matcha);
  margin: 0.35rem 0 0;
}

.skill-card__note {
  font-size: 0.82rem;
  color: var(--color-text-muted);
  margin: 0.4rem 0 0;
  line-height: 1.65;
}

.skills__loading {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--color-text-muted);
}

/* --- mathematical background: massive offscreen Math C (Line-Family Envelope Astroid) --- */
.skills__bg-math {
  position: absolute;
  top: -100px;
  right: -250px;
  width: min(660px, 80vw);
  height: min(660px, 80vw);
  pointer-events: none;
  z-index: -1;
  opacity: 0.14;
}

.envelope-svg {
  width: 100%;
  height: 100%;
  overflow: visible;
}

.envelope-path {
  fill: none;
  stroke: var(--color-matcha);
  stroke-width: 0.5px;
  opacity: 0.75;
  vector-effect: non-scaling-stroke;
}

.envelope-poly {
  fill: none;
  stroke: var(--color-matcha-light);
  stroke-width: 0.65px;
  opacity: 0.5;
  vector-effect: non-scaling-stroke;
}

@media (max-width: 600px) {
  .skills__groups {
    gap: 2.25rem;
  }
  .skills__grid {
    grid-template-columns: repeat(auto-fill, minmax(135px, 1fr));
    gap: 0.6rem;
  }
  .skill-card {
    padding: 0.9rem 1rem;
  }
  .skills__bg-math {
    top: -40px;
    right: -70px;
    width: min(340px, 85vw);
    height: min(340px, 85vw);
    opacity: 0.5;
  }
}