背景图片固定不随页面上下滚动而滚动 ,属性 background-attachment

<div id="testimonials-section" class="text-center">
  
</div>

css:

#testimonials-section {
    background: url(../img/testimonial-bg.jpg);
    background-size: cover;
    background-position: top;
    background-attachment: fixed;
    background-repeat: no-repeat;
    color: #ffffff;
    padding: 80px 0;
}