body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    display: flex;
    flex-direction: column;
    align-items: center;
    background-color: #f0f2f5;
    padding: 20px;
}

h2 {
    color: #333;
}

/* 画板容器 */
.board-container {
    background: white;
    padding: 10px;
    border-radius: 8px;
    box-shadow: 0 4px 15px rgba(0,0,0,0.1);
    position: relative;
    /* 防止移动端选取文本 */
    user-select: none; 
}

/* 画布样式 */
canvas {
    border: 2px solid #ddd;
    border-radius: 4px;
    cursor: crosshair;
    background-color: #fff;
    /* 关键：防止手机端画图时触发浏览器的滚动/刷新行为 */
    touch-action: none; 
    display: block; /* 消除底部微小间隙 */
}

/* 工具栏 */
.toolbar {
    margin-top: 15px;
    display: flex;
    gap: 10px;
    justify-content: center;
}

button {
    padding: 10px 20px;
    border: none;
    border-radius: 5px;
    font-size: 14px;
    cursor: pointer;
    transition: background 0.2s;
    font-weight: 500;
}

.btn-clear {
    background-color: #e74c3c;
    color: white;
}
.btn-clear:hover { background-color: #c0392b; }

.btn-submit {
    background-color: #2ecc71;
    color: white;
}
.btn-submit:hover { background-color: #27ae60; }

/* 反馈状态显示 */
#status {
    margin-top: 10px;
    height: 20px;
    color: #2ecc71;
    font-weight: bold;
    text-align: center;
    font-size: 14px;
}