/* --- 基本設定 --- */
:root {
    --bg-color: #f0f0f0;
    --panel-bg: #ffffff;
    --border-color: #ccc;
    --shadow-color: rgba(0,0,0,0.1);
    --primary-color: #007bff;
    --hover-color: #0056b3;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background-color: var(--bg-color);
    color: #333;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 1rem;
    overflow: hidden;
}

/* --- 主容器佈局 --- */
#game-container {
    display: flex;
    gap: 20px;
    width: 100%;
    max-width: 1600px; /* 可適當加大 */
    height: 90vh;
}

#left-panel {
    display: flex;
    flex-direction: column;
    gap: 20px;
    width: 320px;
    flex-shrink: 0;
}

/* 【修改】右側遊戲區設定 */
#play-area {
    flex-grow: 1;
    position: relative; /* 極為重要！這是所有絕對定位元素的參考點 */
    background-color: #e9e9e9;
    border-radius: 8px;
    box-shadow: inset 0 0 10px rgba(0,0,0,0.1);
    overflow: hide; /* 確保碎片不會跑出遊戲區 */
}

/* --- 控制面板 (左側) --- */
#control-panel, #reference-container {
    background-color: var(--panel-bg);
    border-radius: 8px;
    box-shadow: 0 2px 8px var(--shadow-color);
    padding: 15px;
}

#control-panel h2, #reference-container h3 {
    text-align: center;
    margin-bottom: 15px;
}

.control-group { margin-bottom: 15px; }
.control-group label { font-weight: bold; display: block; margin-bottom: 5px; }

#timer {
    font-size: 1.8em;
    font-weight: bold;
    color: #d9534f;
    text-align: center;
    background: #f9f9f9;
    padding: 5px;
    border-radius: 4px;
}

#difficulty-selector, #post-game-controls { display: flex; gap: 10px; justify-content: center; }

button {
    padding: 10px 15px;
    border: none;
    background-color: var(--primary-color);
    color: white;
    border-radius: 4px;
    cursor: pointer;
    transition: background-color 0.2s;
    font-size: 1em;
}
button:hover { background-color: var(--hover-color); }
#difficulty-selector button.active { background-color: #28a745; box-shadow: inset 0 2px 4px rgba(0,0,0,0.2); }
#game-message { text-align: center; margin-top: 15px; font-weight: bold; min-height: 24px; }

#reference-canvas { max-width: 100%; border-radius: 4px; border: 1px solid var(--border-color); }


/* --- 遊戲區內的元素 --- */
/* 【修改】拼圖板定位在遊戲區中央 */
#puzzle-board {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    border: 2px solid #333;
    box-shadow: 0 0 10px rgba(0,0,0,0.5);
    z-index: 10;
}

/* 【修改】拼圖碎片的樣式 */
.puzzle-piece {
    position: absolute; /* 所有碎片都相對於 #play-area 定位 */
    cursor: grab;
    box-shadow: 0 2px 5px rgba(0,0,0,0.3);
    transition: transform 0.2s ease-out, box-shadow 0.2s ease-out;
    z-index: 20; /* 預設在拼圖板之上 */
}

.puzzle-piece:hover {
    z-index: 998;
    transform: scale(1.1) !important;
}

.dragging {
    cursor: grabbing;
    z-index: 999 !important;
    transform: scale(1.15) !important;
    box-shadow: 0 5px 15px rgba(0,0,0,0.4);
    transition: none;
}

.placed {
    pointer-events: none;
    box-shadow: none;
    z-index: 15; /* 放在拼圖板之上，但在可拖曳的碎片之下 */
    transform: rotate(0deg) !important;
}