Menu Hover Style Using HTML5 and CSS3

Creating a Menu Hover style with HTML5 and CSS3.

HTML

 <html>
<head>
    <title>This is Menu</title>
    <link rel="stylesheet" type="text/css" href="menu.css">
    </head>
    <body>
    <ul>
        <li><a href="#">Home</a></li>
        <li><a href="#">About</a></li>
        <li><a href="#">Blog</a></li>
        <li><a href="#">Portfolio</a></li>
        <li><a href="#">Contact</a></li>
        </ul>
   
    </body>
</html>

CSS 

body{
    margin: 0px;
    padding: 0px;
    font-family: serif;
}
ul {
    position: absolute;
    top: 50%;
    left: 50%;
    display:flex;
    transform: translate(-50%,-50%)
}
li{
    list-style: none;
}

a {
    position: relative;
    display: block;
    text-decoration: none;
    text-align: center;
    margin: 0 25px;
    color:#252625;
    font-size: 30px;
    text-transform: uppercase;
    transition: .5s;
    padding: 5px 10px;
   
}
a:before{
    content: "";
    position: absolute;
    bottom: 12px;
    left: 12px;
    width: 12px;
    height: 12px;
    border: 3px solid #ffc107;
    border-width: 0 0 3px 3px;
    transition: .5s;
    opacity: 0;
}
a:after{
    content: "";
    position: absolute;
    top: 12px;
    right: 12px;
    width: 12px;
    height: 12px;
    border: 3px solid #ffc107;
    border-width: 3px 3px 0 0;
    transition: .5s;
    opacity: 0;
}
a:hover{
    color: #fff;
    background-color: #ffc107
}

a:hover:before{
    bottom: -8px;
    left: -8px;
    opacity: 1;
}
a:hover:after{
    top: -8px;
    right: -8px;
    opacity: 1;
}