web前端之不一样的下拉菜单、不选中第一个元素的样式效果、伪类排除第一个元素、符号选择器、hover、not、first、child

效果图

html+css+JS

html

<nav>
    <ul>
        <li class="navli">
            <h4>HTML5</h4>
            <ul class="ulson">
                <li class="lison">HTML5</li>
            </ul>
        </li>
        <li class="navli">
            <h4>CSS3</h4>
            <ul class="ulson">
                <li class="lison">CSS3</li>
                <li class="lison">CSS3</li>
                <li class="lison">CSS3</li>
            </ul>
        </li>
        <li class="navli">
            <h4>JS</h4>
            <ul class="ulson">
                <li class="lison">JS</li>
                <li class="lison">JS</li>
                <li class="lison">JS</li>
                <li class="lison">JS</li>
                <li class="lison">JS</li>
            </ul>
        </li>
        <li class="navli">
            <h4>JQUERY</h4>
            <ul class="ulson">
                <li class="lison">JQUERY</li>
                <li class="lison">JQUERY</li>
                <li class="lison">JQUERY</li>
                <li class="lison">JQUERY</li>
            </ul>
        </li>
        <li class="navli">
            <h4>VUE</h4>
            <ul class="ulson">
                <li class="lison">VUE</li>
                <li class="lison">VUE</li>
                <li class="lison">VUE</li>
            </ul>
        </li>
    </ul>
</nav>

JavaScript

init();

function init() {
    let aH = document.querySelectorAll('h4');
    let aLi = document.querySelectorAll('.lison');
    let anavLi = document.querySelectorAll('.navli');
    let aUl = document.querySelectorAll('.ulson');

    changeColor(aH);
    changeColor(aLi);
    handleLi(anavLi, aUl);

    function handleLi(arr, list) {
        for (let i = 0; i < arr.length; i++) {
            arr[i].onmouseover = () => {
                list[i].style.display = 'block';
            }
            arr[i].onmouseout = () => {
                list[i].style.display = 'none';
            }
        }
    }

    function changeColor(arr) {
        for (let i = 0; i < arr.length; i++) {
            arr[i].onmouseover = function () {
                this.style.backgroundColor = '#ff0000';
            }
            arr[i].onmouseout = function () {
                this.style.backgroundColor = 'transparent';
            }
        }
    }
}

style

* {
    margin: 0;
    padding: 0;
}

body {
    background-color: #333333;
    color: #ffffff;
}

nav {
    width: 350px;
    height: 30px;
    line-height: 30px;
    margin: 50px auto;
    border-radius: 5px;
    box-shadow: 2px 5px 15px rgba(0, 0, 0, .7);
}


h4:hover {
    cursor: pointer;
    border-radius: 5px;
}

nav ul {
    width: 100%;
    list-style: none;
}

.navli {
    float: left;
    width: 70px;
    text-align: center;
    font-size: 14px;
}

.ulson {
    display: none;
    box-shadow: 2px 5px 15px rgba(0, 0, 0, .7);
    border-radius: 3px;
}

li:hover {
    border-radius: 3px;
}

.ulson li:not(:first-child) {
    border-top: 1px dashed #cccccc;
}

html+css

html

<ul class="navul">
    <li class="navli">
        <h4>HTML5</h4>
        <ul class="ulson">
            <li class="lison">HTML5</li>
        </ul>
    </li>
    <li class="navli">
        <h4>CSS3</h4>
        <ul class="ulson">
            <li class="lison">CSS3</li>
            <li class="lison">CSS3</li>
            <li class="lison">CSS3</li>
        </ul>
    </li>
    <li class="navli">
        <h4>JS</h4>
        <ul class="ulson">
            <li class="lison">JS</li>
            <li class="lison">JS</li>
            <li class="lison">JS</li>
            <li class="lison">JS</li>
            <li class="lison">JS</li>
        </ul>
    </li>
    <li class="navli">
        <h4>JQUERY</h4>
        <ul class="ulson">
            <li class="lison">JQUERY</li>
            <li class="lison">JQUERY</li>
            <li class="lison">JQUERY</li>
            <li class="lison">JQUERY</li>
        </ul>
    </li>
    <li class="navli">
        <h4>VUE</h4>
        <ul class="ulson">
            <li class="lison">VUE</li>
            <li class="lison">VUE</li>
            <li class="lison">VUE</li>
        </ul>
    </li>

    <div class="hk"></div>
</ul>

style

* {
    margin: 0;
    padding: 0;
    list-style: none;
}

body {
    width: 100vw;
    height: 100vh;
    display: flex;
    justify-content: center;
    background-color: #333333;
    color: #ffffff;
}

.navul {
    position: relative;
    width: 350px;
    height: 30px;
    line-height: 30px;
    display: flex;
    margin-top: 50px;
    border-radius: 5px;
    font-size: 14px;
    box-shadow: 2px 5px 15px rgba(0, 0, 0, .7);
}

.navli {
    width: 70px;
    text-align: center;
}

.navli:hover .ulson {
    display: block;
}

.ulson {
    display: none;
    box-shadow: 2px 5px 15px rgba(0, 0, 0, .7);
    border-radius: 5px;
}

.ulson li:not(:first-child) {
    border-top: 1px dashed #cccccc;
}

.lison:hover {
    background-color: rgba(100, 100, 130, .8);
    border-radius: 5px;
}

.hk {
    position: absolute;
    left: 0;
    width: 70px;
    height: 30px;
    background-color: rgba(100, 100, 130, .5);
    border-radius: 5px;
    z-index: -999;
    transition: .5s;
    display: none;
}

.navli:nth-child(1):hover~.hk {
    display: block;
    left: 0;
}

.navli:nth-child(2):hover~.hk {
    display: block;
    left: 70px;
}

.navli:nth-child(3):hover~.hk {
    display: block;
    left: 140px;
}

.navli:nth-child(4):hover~.hk {
    display: block;
    left: 210px;
}

.navli:nth-child(5):hover~.hk {
    display: block;
    left: 280px;
}