/* Global design tokens */
:root {
  --bg-primary: hsl(230, 15%, 10%);
  --bg-card: hsla(230, 15%, 15%, 0.9);
  --accent-cyan: hsl(180, 80%, 55%);
  --accent-magenta: hsl(300, 80%, 55%);
  --text-primary: hsl(0, 0%, 95%);
  --text-secondary: hsl(0, 0%, 70%);
  --glow-size: 0.3rem;
  --transition: 0.2s ease-out;
}

/* Reset & base */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
body {
  font-family: 'Inter', sans-serif;
  background: radial-gradient(circle at 20% 20%, var(--accent-cyan), var(--bg-primary) 70%);
  color: var(--text-primary);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: flex-start;
  padding: 2rem;
}
header h1 {
  font-size: 2.5rem;
  text-align: center;
  margin-bottom: 1rem;
  background: linear-gradient(45deg, var(--accent-cyan), var(--accent-magenta));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

/* Core button */
.glow-btn {
  background: var(--bg-card);
  border: none;
  border-radius: 1rem;
  padding: 1.5rem 2rem;
  display: flex;
  align-items: center;
  gap: 0.8rem;
  cursor: pointer;
  font-size: 1.2rem;
  color: var(--text-primary);
  box-shadow: 0 0 var(--glow-size) var(--accent-cyan);
  transition: var(--transition);
}
.glow-btn:hover {
  transform: scale(1.05);
  box-shadow: 0 0 1rem var(--accent-magenta);
}
.core-icon {
  width: 2.5rem;
  height: 2.5rem;
  animation: pulse 2s infinite;
}
@keyframes pulse {
  0% { filter: drop-shadow(0 0 4px var(--accent-cyan)); }
  50% { filter: drop-shadow(0 0 12px var(--accent-magenta)); }
  100% { filter: drop-shadow(0 0 4px var(--accent-cyan)); }
}
.resource-display {
  margin-top: 0.5rem;
  font-size: 1.1rem;
  color: var(--text-secondary);
}

/* Upgrade cards */
.cards-container {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1rem;
  margin-top: 2rem;
  width: 100%;
  max-width: 900px;
}
.upgrade-card {
  background: var(--bg-card);
  border-radius: 0.8rem;
  padding: 1rem;
  backdrop-filter: blur(6px);
  border: 1px solid hsla(0,0%,100%,0.05);
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  transition: var(--transition);
}
.upgrade-card:hover {
  transform: translateY(-3px);
  border-color: var(--accent-cyan);
}
.upgrade-card button {
  background: var(--accent-cyan);
  border: none;
  color: #000;
  padding: 0.5rem;
  border-radius: 0.4rem;
  cursor: pointer;
  font-weight: 600;
}
.upgrade-card button:disabled {
  background: var(--text-secondary);
  cursor: not-allowed;
}

footer {
  margin-top: auto;
  font-size: 0.8rem;
  color: var(--text-secondary);
}