.ruler {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    user-select: none;
    z-index: 1000;
    border-radius: 12px;
    background: rgba(255, 255, 255, 0.05);
    backdrop-filter: blur(10px);
    box-shadow: 0 4px 30px rgba(0, 0, 0, 0.2);
    border: 1px solid rgba(255, 255, 255, 0.2);
    transition: transform 0.2s ease, box-shadow 0.2s ease;
    cursor: grab;
    width: 80vw;
    max-width: 600px;
}

.ruler:active {
    cursor: grabbing;
    box-shadow: 0 8px 40px rgba(0, 255, 255, 0.4);
    transform: translate(-50%, -50%) scale(1.02);
}

canvas {
    display: block;
    border-radius: 12px;
    width: 100%;
    height: 60px;
}

.controls {
    text-align: center;
    margin-bottom: 1em;
}

.controls button {
    padding: 0.6em 1.5em;
    margin: 0.5em;
    font-size: 1em;
    border: 1px solid rgba(0,255,255,0.6);
    border-radius: 8px;
    background: rgba(0,0,0,0.4);
    color: #0ff;
    text-shadow: 0 0 8px #0ff;
    cursor: pointer;
    transition: all 0.3s ease;
    backdrop-filter: blur(5px);
}

.controls button:hover {
    background: rgba(0,255,255,0.1);
    color: #fff;
    box-shadow: 0 0 12px #0ff;
}

/* 默认隐藏旋转按钮 */
#rotateBtn {
    display: none;
}

/* 手机端显示旋转按钮 */
@media (max-width: 768px) {
    #rotateBtn {
        display: inline-block;
    }
    canvas {
        height: 50px;
    }
}