:root {
  --bg-color: #0f131a;
  --panel-bg: #181f29;
  --text-primary: #e8e8e8;
  --accent: #4a90e2;
  --dark-sq: #b58863;
  --light-sq: #f0d9b5;
  --selected-sq: rgba(255, 255, 51, 0.6);
}

* { 
  box-sizing: border-box; 
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif; 
  user-select: none; 
  -webkit-tap-highlight-color: transparent; 
}

/* Allow text selection ONLY in text blocks */
.install-guide p, .install-guide h3, .credits-text, .modal-content h2 {
  user-select: text;
}

body { margin: 0; padding: 0; background: var(--bg-color); color: var(--text-primary); }

.menu-container { 
  display: flex; flex-direction: column; align-items: center; justify-content: center; 
  min-height: 100vh; text-align: center; padding: 2rem 1rem; 
}
.menu-container h1 { font-size: clamp(2.5rem, 8vw, 3.5rem); margin-bottom: 0.5rem; }

.btn { 
  border: none; padding: 16px 20px; border-radius: 8px; cursor: pointer; 
  font-weight: bold; font-size: 1.1rem; background: #333; color: #fff; 
  transition: all 0.2s ease; text-decoration: none; display: inline-block; 
}
.btn:active { filter: brightness(0.8); transform: scale(0.97); }
.primary-btn { background: var(--accent); margin-bottom: 2rem; font-size: 1.2rem; }

.install-guide { max-width: 600px; text-align: left; width: 100%; margin-top: 20px; }
.os-card { background: var(--panel-bg); padding: 15px; border-radius: 8px; margin-bottom: 10px; }
.os-card h3 { margin: 0 0 5px 0; }
.os-card p { margin: 0; font-size: 0.9rem; color: #bbb; line-height: 1.4; }

.app-container { display: flex; flex-direction: row; min-height: 100vh; }

.board-area { flex: 2; display: flex; flex-direction: column; align-items: center; justify-content: center; padding: 20px; min-width: 320px; }
.sidebar { flex: 1; background: var(--panel-bg); display: flex; flex-direction: column; min-width: 300px; border-left: 2px solid #2c3645; }

.status-bar { font-size: 1.5rem; font-weight: bold; margin-bottom: 15px; padding: 10px 20px; border-radius: 8px; background: rgba(0,0,0,0.3); }

.chessboard { 
  display: grid; grid-template-columns: repeat(8, 1fr); grid-template-rows: repeat(8, 1fr);
  width: 100%; max-width: 550px; aspect-ratio: 1; border: 8px solid #2a2a2a; border-radius: 6px; box-shadow: 0 10px 30px rgba(0,0,0,0.6);
  transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1); 
}
.chessboard.flipped { transform: rotate(180deg); }
.chessboard.flipped .square { transform: rotate(-180deg); }

.square { width: 100%; height: 100%; display: flex; justify-content: center; align-items: center; cursor: pointer; position: relative; transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1); }
.square.light { background-color: var(--light-sq); }
.square.dark { background-color: var(--dark-sq); }
.square.selected::after { content:''; position:absolute; top:0;left:0;right:0;bottom:0; background: var(--selected-sq); box-shadow: inset 0 0 10px rgba(0,0,0,0.5); }
.square.valid-move::before { content:''; position:absolute; width: 30%; height: 30%; background: rgba(0,0,0,0.2); border-radius: 50%; }
.square svg { width: 85%; height: 85%; z-index: 2; pointer-events: none; filter: drop-shadow(0px 3px 3px rgba(0,0,0,0.5)); }

.tabs { display: flex; border-bottom: 2px solid #2c3645; flex-shrink: 0; }
.tab-btn { flex: 1; padding: 18px 15px; background: none; border: none; color: #aaa; cursor: pointer; font-size: 1.05rem; font-weight: bold; }
.tab-btn.active { color: #fff; border-bottom: 3px solid var(--accent); }
.tab-content { padding: 20px; flex: 1; }

.toggle-container { display: flex; align-items: center; cursor: pointer; font-size: 1.1rem; font-weight: 500; position: relative; padding: 10px 0; }
.toggle-container input { opacity: 0; width: 0; height: 0; }
.checkmark { width: 44px; height: 24px; background: #555; border-radius: 20px; margin-right: 12px; position: relative; transition: 0.3s; flex-shrink: 0; }
.checkmark::after { content: ''; position: absolute; width: 20px; height: 20px; background: #fff; border-radius: 50%; top: 2px; left: 2px; transition: 0.3s; }
.toggle-container input:checked ~ .checkmark { background: var(--accent); }
.toggle-container input:checked ~ .checkmark::after { transform: translateX(20px); }
.small-text { font-size: 0.85rem; color: #999; margin-top: 4px; line-height: 1.4; }

.credits-text a { color: var(--accent); text-decoration: none; font-weight: bold; }
.badge-wrapper { margin-top: 20px; }
.badge-wrapper svg { max-width: 100%; height: auto; }
hr { border: 1px solid #2c3645; margin: 20px 0; }

/* Modal Game Over Styles */
.modal {
  position: fixed; top: 0; left: 0; right: 0; bottom: 0;
  background: rgba(0,0,0,0.85); z-index: 1000;
  display: flex; align-items: center; justify-content: center;
}
.modal-content {
  background: var(--panel-bg); padding: 30px; border-radius: 12px;
  text-align: center; border: 2px solid var(--accent);
  box-shadow: 0 10px 40px rgba(0,0,0,0.8); min-width: 280px;
}
.modal-content h2 { margin-top: 0; font-size: 2.2rem; margin-bottom: 25px; color: #fff; }

@media (max-width: 768px) {
  .app-container { flex-direction: column; }
  .board-area { flex: none; height: auto; padding: 10px 5px; min-width: 100%; }
  .chessboard { border-width: 4px; max-width: 100%; width: 95vw; height: 95vw; }
  .status-bar { font-size: 1.2rem; padding: 8px 16px; margin-bottom: 10px; }
  .sidebar { flex: 1; border-left: none; border-top: 2px solid #2c3645; min-width: 100%; }
  .tab-content { padding: 15px; }
}