MUI导航栏透明渐变----原生JS实现

body,p,h1{margin: 0;}
.module-layer{
    width: 100%;
    position: fixed;
    top: 0;
    left: 0;
    z-index: 100000;
}
.module-layer-content{
    position: relative;
    min-width: 320px;
    max-width: 750px;
    width: 100%;
    margin: 0 auto;
    background-color: rgba(255, 0, 0, 0.9);
}
.module-layer-bg{
    width: 100%;
    height: 100%;
    background: #000;
    opacity: .7;
    position: absolute;
    top: 0;
    left: 0;
    z-index: -1;
}
.layer-head-name{
    height: 50px;
    line-height: 50px;
    text-align: center;
    padding: 0 50px;
    font-size: 20px;
}
.layer-return,.layer-share{
    width: 50px;
    height: 50px;
    line-height: 50px;
    text-align: center;
    position: absolute;
    top:0;
    z-index: 1;
}
.layer-return{left: 0;}
.layer-share{right: 0;}
.fixed-layer{
    height: 100%;
    display: none;
    z-index: 100001;
}
.relative-layer{height: 100%;}
.layer-content{
    padding:3%;
    position: relative;
    top: 20%;
}
.layer-close{
    width: 2rem;
    height: 2rem;
    position: absolute;
    top:3%;
    right: 3%;
}
.pr {
    position:relative;
}
#shop-input::-webkit-input-placeholder {
    color:#fff;
}
#shop-input:-moz-placeholder {
    color:#fff;
}
#shop-input::-moz-placeholder {
    color:#fff;
}
#shop-input:-ms-input-placeholder {
    color:#fff;
}
#shop-input {
    border:none;
    outline:none;
    background:transparent;
}
.search-box {
    height:30px;
    border-radius:20px;
    top:10px;
    overflow:hidden;
    z-index:10;
}
.search-box:after {
    content:'';
    display:block;
    width:100%;
    height:30px;
    background:#fff;
    opacity:.5;
    position:absolute;
    top:0;
    left:0px;
    z-index:-1;
}
#shop-input {
    height:28px;
    line-height:28px;
    font-size:16px;
    position:absolute;
    top:0;
    left:30px;
}
.shop-search {
    width:16px;
    height:16px;
    position:absolute;
    top:7px;
    left:6px;
}
.layer-return{
    background: url(images/return.png) no-repeat center center/12px 20px;
}
.layer-share{
    background: url(images/share.png) no-repeat center center/20px 30px;
}
a {
  -webkit-tap-highlight-color: transparent;
  -webkit-touch-callout: none;
  -webkit-user-select: none;
}
.module-content{
    min-width: 320px;
    max-width: 750px;
    width: 100%;
    margin: 0 auto;
    background: #fff;
}
.module-content div:first-child img{margin-top: 0;}
.module-content div img{
    display: block;
    width: 100%;
    margin-top: 10px;
}

<header class="module-layer">
    <div class="module-layer-content">
        <p class="layer-return"></p>
        <h1 class="layer-head-name">
            <div class="pr search-box">
                <img class="shop-search" src="images/search.png"/>
                <input id="shop-input" type="text" placeholder="搜索店内商品" value="" />
            </div>
        </h1>
        <p class="layer-share"></p>
    </div>
</header>
<div class="module-content">
    <div><img src="images/banner.png"/></div> 
    <div><img src="images/banner1.png"/></div> 
    <div><img src="images/banner3.png"/></div>
    <div><img src="images/banner4.jpg"/></div>
    <div><img src="images/banner5.png"/></div>
    <div><img src="images/banner6.png"/></div>
    <div><img src="images/banner7.jpg"/></div>
    <div><img src="images/banner8.jpg"/></div>
</div>

(function(){
    //获取滚动条当前位置
    function getScrollTop(){  
    　　var scrollTop = 0, bodyScrollTop = 0, documentScrollTop = 0;  
    　　if(document.body){  
    　　　　bodyScrollTop = document.body.scrollTop; 
    　　}  
    　　if(document.documentElement){  
    　　　　documentScrollTop = document.documentElement.scrollTop; 
    　　}  
    　　scrollTop = (bodyScrollTop - documentScrollTop > 0) ? bodyScrollTop : documentScrollTop;  
    　　return scrollTop;  
    }
    //获取CSS样式
    function getStyle(element, attr){
        if(element.currentStyle){
            return element.currentStyle[attr];
        }else{
            return window.getComputedStyle(element,null)[attr];
        }
    }
    //获取原始backgroundColor值
    var color = getStyle(document.getElementsByClassName('module-layer-content')[0],'backgroundColor');
    //取到RGB
    var colorRgb = color.substring(0,color.lastIndexOf(',') + 1);
    //取到A
    var colorA = color.substring(color.lastIndexOf(',') + 1,color.length - 1);
    //对A判断，如果最终值小于0.9，直接设置为1
    if(colorA < 0.9){colorA = 1;}
    //设置背景色的A的函数
    var setCoverOpacity = function() {
        document.getElementsByClassName('module-layer-content')[0].style.background = colorRgb + (((getScrollTop() / 550) > colorA) ? colorA : (getScrollTop() / 550)) + ')';
    }
    //初始化函数
    setCoverOpacity();
    //绑定滚动监听事件
    window.addEventListener('scroll',setCoverOpacity,false);
}())