看看他的CSS就会知道了

.input {
    height: 20px;
    clip: rect( );
    color: #333333;
    font-family: "Arial", "Helvetica", "sans-serif";
    text-decoration: none;
    text-transform: uppercase;
    text-align: center;
    border-top: 0px solid #CCCCCC;
    border-right: 0px solid #CCCCCC;
    border-bottom: 1px solid #CCCCCC;
    border-left: 0px solid #CCCCCC;
}

要试着分析源代码