:root {
  --bg-primary: #0d1117;
  --bg-secondary: #161b22;
  --bg-card: #1c2128;
  --text-primary: #e6edf3;
  --text-secondary: #8b949e;
  --accent: #58a6ff;
  --accent-hover: #79c0ff;
  --border: #30363d;
  --element-bg: #21262d;
  --element-border: #444c56;
}

* { margin: 0; padding: 0; box-sizing: border-box; }

body {
  background: var(--bg-primary);
  color: var(--text-primary);
  font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 20px;
}

.container {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 32px;
  max-width: 800px;
  width: 100%;
  box-shadow: 0 8px 32px rgba(0,0,0,0.4);
}

h1 {
  font-size: 1.8rem;
  margin-bottom: 24px;
  text-align: center;
  background: linear-gradient(135deg, var(--accent), #a371f7);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

input[type="text"] {
  width: 100%;
  padding: 14px 18px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 10px;
  color: var(--text-primary);
  font-size: 1.1rem;
  outline: none;
  transition: border-color 0.2s;
}

input[type="text"]:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px rgba(88,166,255,0.15);
}

button {
  margin-top: 16px;
  padding: 14px 28px;
  background: var(--accent);
  color: #0d1117;
  border: none;
  border-radius: 10px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s;
  width: 100%;
}

button:hover {
  background: var(--accent-hover);
  transform: translateY(-1px);
}

button:active { transform: translateY(0); }

#downloadBtn { background: #238636; color: #fff; }
#downloadBtn:hover { background: #2ea043; }

.canvas-wrapper {
  margin-top: 24px;
  /* Cho phép cuộn ngang khi ảnh rộng hơn container */
  overflow-x: auto;
  overflow-y: hidden;
  padding: 16px 8px;
  /* Hiệu ứng mờ 2 bên để gợi ý còn nội dung */
  background:
    linear-gradient(to right, var(--bg-secondary) 0%, transparent 24px),
    linear-gradient(to left, var(--bg-secondary) 0%, transparent 24px);
  background-attachment: local, local;
  background-position: left, right;
  background-repeat: no-repeat;
  background-size: 24px 100%, 24px 100%;
  border-radius: 10px;
  /* Thanh cuộn mảnh, hợp dark theme */
  scrollbar-width: thin;
  scrollbar-color: var(--border) transparent;
}

/* Thanh cuộn cho Chrome/Edge/Safari */
.canvas-wrapper::-webkit-scrollbar {
  height: 8px;
}
.canvas-wrapper::-webkit-scrollbar-track {
  background: transparent;
}
.canvas-wrapper::-webkit-scrollbar-thumb {
  background: var(--border);
  border-radius: 4px;
}
.canvas-wrapper::-webkit-scrollbar-thumb:hover {
  background: var(--accent);
}

canvas {
  border-radius: 12px;
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.5);
  /* QUAN TRỌNG: bỏ max-width: 100% để canvas giữ đúng kích thước */
  max-width: none;
  height: auto;
  display: block;
  /* Không cho canvas co lại trong flex container */
  flex-shrink: 0;
}

.canvas-wrapper {
  /* ... các thuộc tính ở trên ... */
  position: relative;
  display: flex;
  align-items: center;
  gap: 8px;
}

.scroll-btn {
  position: sticky;
  flex-shrink: 0;
  width: 36px;
  height: 36px;
  margin: 0;
  padding: 0;
  background: rgba(88, 166, 255, 0.15);
  color: var(--accent);
  border: 1px solid var(--border);
  border-radius: 50%;
  font-size: 1.4rem;
  font-weight: bold;
  line-height: 1;
  cursor: pointer;
  transition: all 0.2s;
  z-index: 2;
}

.scroll-btn:hover {
  background: var(--accent);
  color: #0d1117;
}

.scroll-btn:disabled {
  opacity: 0.3;
  cursor: not-allowed;
}

.scroll-btn#scrollLeft  { left: 8px; }
.scroll-btn#scrollRight { right: 8px; }

.canvas-wrapper:not(:has(canvas)) .scroll-btn { display: none; }