:root{
  --bg-start:#f5f7fa;
  --bg-end:#e8f0ff;
  --accent:#1e90ff;
  --card-bg:#ffffff;
  --text:#222;
  --muted:#6b7280;
  --radius:12px;
  --shadow: 0 6px 18px rgba(16,24,40,0.08);
  --shadow-hover: 0 12px 30px rgba(16,24,40,0.12);
  font-family: "Noto Sans JP", "Hiragino Kaku Gothic ProN", "Yu Gothic", system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial;
}

html,body{
  height:100%;
  margin:0;
  color:var(--text);
  background: linear-gradient(180deg,var(--bg-start),var(--bg-end));
  -webkit-font-smoothing:antialiased;
  -moz-osx-font-smoothing:grayscale;
}

/* Header */
.header{
  display:flex;
  align-items:center;
  justify-content:space-between;
  padding:20px 28px;
  max-width:1100px;
  margin:0 auto;
}
.logo{
  display:flex;
  align-items:center;
  gap:12px;
}
.logo .mark{
  width:40px;
  height:40px;
  border-radius:8px;
  background:linear-gradient(135deg,var(--accent),#6fb3ff);
  box-shadow:var(--shadow);
  display:flex;
  align-items:center;
  justify-content:center;
  color:white;
  font-weight:700;
  font-size:18px;
}
.logo .title{
  font-weight:700;
  font-size:18px;
  letter-spacing:0.2px;
}
.login-btn{
  background:transparent;
  border:2px solid rgba(34,34,34,0.08);
  padding:8px 14px;
  border-radius:10px;
  color:var(--text);
  font-weight:600;
  cursor:pointer;
  transition:all .18s ease;
}
.login-btn:hover{
  transform:translateY(-2px);
  box-shadow:var(--shadow);
}

/* Main container */
.container{
  max-width:1100px;
  margin:36px auto;
  padding:24px;
  display:flex;
  flex-direction:column;
  gap:28px;
  align-items:center;
}
.hero-title{
  font-size:28px;
  font-weight:800;
  margin:6px 0 0 0;
  text-align:center;
}
.hero-sub{
  color:var(--muted);
  margin-top:6px;
  text-align:center;
}

/* Cards layout */
.cards{
  display:grid;
  grid-template-columns:repeat(3,1fr);
  gap:20px;
  width:100%;
  margin-top:18px;
}
.card{
  background:var(--card-bg);
  border-radius:var(--radius);
  padding:28px 20px;
  box-shadow:var(--shadow);
  display:flex;
  flex-direction:column;
  align-items:center;
  justify-content:center;
  gap:12px;
  transition:transform .18s ease, box-shadow .18s ease;
  cursor:pointer;
  min-height:160px;
  text-align:center;
  outline: none;
}
.card:hover,
.card:focus{
  transform:translateY(-6px) scale(1.02);
  box-shadow:var(--shadow-hover);
}
.game-title{
  font-size:22px;
  font-weight:800;
  letter-spacing:0.4px;
}
.game-desc{
  color:var(--muted);
  font-size:13px;
}

/* Accent for each card */
.card[data-game="2048"] .game-title{ color:#0f172a; }
.card[data-game="tetris"] .game-title{ color:var(--accent); }
.card[data-game="othello"] .game-title{ color:#0b6b3a; }

/* Responsive */
@media (max-width:900px){
  .cards{ grid-template-columns:repeat(2,1fr); }
}
@media (max-width:600px){
  .header{ padding:14px; }
  .cards{ grid-template-columns:1fr; gap:14px; }
  .card{ padding:20px; min-height:120px; }
  .hero-title{ font-size:22px; }
}

/* Small utility */
.small-note{ font-size:12px; color:var(--muted); margin-top:6px; }