案例-三角形（CSS3）

<!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>案例-三角形</title>
    <style>
        div {
            position: relative;
            width: 249px;
            height: 35px;
            border: 1px solid #000;
        }

        div::after {

            content: "";
            position: absolute;
            top: 8px;
            right: 15px;
            width: 10px;
            height: 10px;
            border-right: 1px solid #000;
            border-bottom: 1px solid #000;
            transform: rotate(45deg);
            transition: all 0.2s;


        }

        /*   鼠标经过div 里面的三角旋转 */
        div:hover::after {
            transform: rotate(225deg);
        }