一补充

1 画三角形

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 0;
            border: 5px red solid;
            /* 设置顶部边框线透明 */
            border-top-color: transparent;
            /* 设置左部边框线透明 */
            border-left-color: transparent;
            /* 设置右部边框线透明 */
            border-right-color: transparent;
        }
    </style>
</head>
<body>
    <div class="box"></div>
</body>
</html>

2 伪元素选择器

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 200px;
            height: 200px;
            border: 1px red solid;
        }
        /* 
            伪元素选择器
                作用:在div内部创建一个伪元素
                before:在div主体内容之前创建伪元素
                after:在div主体内容之后创建伪元素
        
        */
        .box::before{
            /* content不能省略 */
            content: "";
            /* display用来表示元素的类型 */
            display: block;
            width: 50px;
            height: 50px;
            background-color: green;
        }

        .box::after{
            content: "";
            display: block;
            width: 50px;
            height: 50px;
            background-color: blue;
        }
    </style>
</head>
<body>
    <div class="box">
        我是一个div
    </div>
</body>
</html>

二定位案例

案例1-贯穿案例-回到顶部

案例2-贯穿案例-二维码弹窗

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>

        .icon-ewm-box img{
            width: 80px;
            height: 80px; 
        }
        .ewm-fa{
            position: relative;
        }
        .icon-ewm-box{
            width: 80px;
            height: 80px;
            position: absolute;
            top: 20px;
            left: -30px;
            display: none;
        }
        /* 用伪元素画三角请 */
        .icon-ewm-box::before{
            content: "";
            display: block;
            width: 0px;
            border: 5px solid red;
            margin: 0 auto;
            border-left-color: transparent;
            border-right-color: transparent;
            border-top-color: transparent;
        }
        /* 移动鼠标 显示三角形 */
        .ewm-fa:hover .icon-ewm-box{
            display: block;
        }
    </style>
</head>
<body>
    <div class="icon">
        <img src="./images/grzx.png" alt="">
        <a class="ewm-fa" href="">
            <img src="./images/ewm.png" alt="">
            <div class="icon-ewm-box">
                <img src="./images/smewm.png" alt="">
            </div>
        </a>
        <img src="./images/gwc.png" alt="">
    </div>
</body>
</html>

案例3-二级下拉菜单

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 一级菜单 */
        .one-menu{
            position: relative;
        }

        .one-menu > li{
            /* 去除无序列表列表项的小圆点 */
            list-style: none;
            background-color: aqua;
            width: 50px;
            margin: 20px 0;
        }

        /* 二级菜单 */
        .two-menu {
            position: absolute;
            top: 0;
            left: 100px;
            /* 让二级菜单影藏 */
            display: none;
        }
        .two-menu li{
            width: 100px;
            background-color: pink;
            list-style: none;
        }

        .one-li:hover .two-menu{
            display: block;
        }
    </style>
</head>
<body>
    
    <ul class="one-menu">
        <li class="one-li">
            手机
            <ul class="two-menu">
                <li>红米手机</li>
                <li>oppo手机</li>
            </ul>
        </li>

        <li class="one-li">
            家电
            <ul class="two-menu">
                <li>小米电视</li>
                <li>格力空调</li>
            </ul>
        
        </li>
        <li class="one-li">
            粮油
            <ul class="two-menu">
                <li>大米</li>
                <li>食用油</li>
            </ul>
        </li>
    </ul>


</body>
</html>

案例4-贯穿案例-二级下拉菜单

三 CSS动画

1 阴影效果

box-shadow: 水平偏移量 垂直偏移量 模糊度  阴影颜色 
box-shadow: 10px 10px 10px red

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 200px;
            height: 200px;
            border: 1px red solid;
            /*  box-shadow:水平偏移量  垂直偏移量  模糊度 颜色   */
            box-shadow: 10px 10px 10px red;
        }
    </style>
</head>
<body>
    <div class="box"></div>
</body>
</html>

2 背景渐变

background: linear-gradient(red,green,blue);

基本案例

    <style>
        .box{
            width: 300px;
            height: 200px;
            background: linear-gradient(red,green,blue);
        }
    </style>
    <div class="box"></div>

色标

色标：在颜色的后面设置颜色的显示范围，控制每一个颜色到底占多少位置

    <style>
        .box{
            width: 300px;
            height: 200px;
            /* 0%~20%是红色，20%~40%是红色到绿色的渐变，40%~70%是绿色，70%~100%是蓝色 */
            background: linear-gradient(red 0% 20%,green 40% 70%,blue 70% 100%);
        }
    </style>
    <div class="box"></div>

方向

background:linear-gradient(角度,起始颜色,结束颜色)

方向可以用角度 30deg表示,也可以用如下英文单词表示

英文单词
to top	从下到上
to bottom	从上到下
to right	从左到右
to left	从右到左

如：

        /* 渐变方向 */
        .box3{
            width: 200px;
            height: 200px;
            border: 1px black solid;
            /* 渐变方向使用角度表示 */
            /* background: linear-gradient(45deg,red 0% 50%,green 60% 80%,blue); */
            /* 
                渐变方向还可以使用英文单词表示
                to top
                to bottom
                to left
                to right
             */
            background: linear-gradient(to right,red 0% 50%,green 60% 80%,blue); 
        }
        
        <div class="box3"></div>

案例-利用渐变色使文字显示的更清晰

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 100%;
            height: 400px;
            background-image: url("http://img.crawler.qq.com/lolwebschool/0/JAutoCMS_LOLWeb_7b19c73a1974944397b300ee3a739097/0");
        }
        .box div{
            height: 100%;
            color: white;
            text-align: center;
            font-size: 25px;
            background: linear-gradient(to bottom,rgba(0,0,0,0.5),rgba(0,0,0,0.1));
        }
    </style>
</head>
<body>
    <div class="box">
        <div>
            游戏下载
            新手指引
            资料库
            云顶之弈
            攻略中心
            开发者基地
            海克斯战利品库
            英雄联盟宇宙
            点券充值
        </div>
    </div>
</body>
</html>

3 过渡

css3给我们提供的某种动态的效果，当元素从一种样式转换成另一种样式时，使其平滑过渡
一般情况下来说，过渡都是搭配hover来使用的

案例1-从背景过度到文字

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .top{
            width: 50px;
            height: 50px;
            border: 1px gray solid;
            background-image: url("./img/gt1.png");
            background-repeat: no-repeat;
            background-position: center;
        }

        .top div{
            width: 50px;
            height: 50px;
            background-color: #900000;
            color: white;
            opacity: 0;
            /* 过度 */
            /* 元素哪些属性过度 */
            transition-property: all;
            /* 过度时间 */
            transition-duration: 1s;
        }

        .top:hover div{
            opacity: 1;
        }

    </style>
</head>
<body>
    <div class="top">
        <div>去购物</div>
    </div>
</body>
</html>

案例2-贯穿项目-二级菜单

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        ul{
            list-style: none;
            display: flex;
            position: relative;
        }
        li{
            margin: 0 20px;
        }
        /* 设置div的初始样式 */
        .list1,.list2{
            position: absolute;
            width: 400px;
            height: 0px;
            /* 溢出隐藏 */
            overflow: hidden;
            /* 过度 transition: 过度属性 过度时间  */
            transition: all 1s;
        }
        /* 搭配hover实现过度 */
        li:hover .list1{
            height: 300px;
        }
        li:hover .list2{
            height: 100px;
        }
    </style>
</head>
<body>

    <ul>
        <li>
            <a href="#">所有商品</a>
            <div class="list1">
                <img src="./images/nav1.jpg" alt="">  
                <img src="./images/nav2.jpg" alt="">  
            </div>
        </li>
        <li>
            <a href="#">装饰摆件</a>
            <div class="list2">
                插画花艺 千花花瓶
            </div>
        </li>
    </ul>
</body>
</html>