<a href="#">
    <span class="text">Hover Over Me</span>
    <span class="btnBefore"></span>
    <span class="btnAfter"></span>
</a>
body {
    padding: 10px;
    background: #f6f6f6;
    color: #000;
    font-size: 24px;
    font-family: arial;
}

a {
    float: left;
    border-radius: 5px;
    margin-top: 10px;
    position: relative;
    z-index: 1;
    overflow: hidden;
    min-width: 50px;
    display: table;
    padding: 5px 10px;
    border: none;
    -webkit-transition: all 0.5s ease-out;
    -moz-transition: all 0.5s ease-out;
    -ms-transition: all 0.5s ease-out;
    -o-transition: all 0.5s ease-out;
    transition: all 0.5s ease-out;
    text-align: center;
    color: #777;
    text-decoration: none;
}
a:hover {
    background-color: #f1f1f1 !important;
}

span {
    position: relative;
    z-index: 1;
    line-height: 24px;
    transition: 0.3s ease;
    -webkit-transition: 0.3s ease;
    -moz-transition: 0.3s ease;
    -o-transition: 0.3s ease;
    -ms-transition: 0.3s ease;
}
a:hover span {
    color: #5a5a5a;
}
.btnBefore, .btnAfter {
    content: '';
    position: absolute;
    height: 0;
    width: 0;
    border: solid #000;
    border-width: 0;
    border-radius: 0;
    transition: 0;
    -webkit-transition: 0;
    -moz-transition: 0;
    -o-transition: 0;
    -ms-transition: 0;
    box-sizing: border-box;
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    border-color: #FF6600;
    border-radius: 5px;
}
a .btnBefore {
    right: 0;
    bottom: 0;
}
a .btnAfter {
    left: 0;
    top: 0;
}
a:hover .btnBefore {
    border-width: 0 0 1px 1px;
}
a:hover .btnAfter {
    border-width: 1px 1px 0 0;
}

a:hover .btnAfter, a:hover .btnBefore {
height: 100%;
width: 100%;
transition: width 0.5s ease, height 0.5s ease 0.5s, border-top-right-radius 0.1s ease 0.4s, border-bottom-left-radius 0.1s ease 0.4s, border-bottom-right-radius 0.1s ease 0.9s, border-top-left-radius 0.1s ease 0.9s;
-webkit-transition: width 0.5s ease, height 0.5s ease 0.5s, border-top-right-radius 0.1s ease 0.4s, border-bottom-left-radius 0.1s ease 0.4s, border-bottom-right-radius 0.1s ease 0.9s, border-top-left-radius 0.1s ease 0.9s;
-moz-transition: width 0.5s ease, height 0.5s ease 0.5s, border-top-right-radius 0.1s ease 0.4s, border-bottom-left-radius 0.1s ease 0.4s, border-bottom-right-radius 0.1s ease 0.9s, border-top-left-radius 0.1s ease 0.9s;
-o-transition: width 0.5s ease, height 0.5s ease 0.5s, border-top-right-radius 0.1s ease 0.4s, border-bottom-left-radius 0.1s ease 0.4s, border-bottom-right-radius 0.1s ease 0.9s, border-top-left-radius 0.1s ease 0.9s;
-ms-transition: width 0.5s ease, height 0.5s ease 0.5s, border-top-right-radius 0.1s ease 0.4s, border-bottom-left-radius 0.1s ease 0.4s, border-bottom-right-radius 0.1s ease 0.9s, border-top-left-radius 0.1s ease 0.9s;
}

External CSS

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External JavaScript

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