.custom-button{color:red;width:200px;height:50px;background:#fff;position:relative;display:flex;align-items:center;justify-content:center;cursor:pointer}.custom-button:before{content:"";position:absolute;left:0;top:0;width:0;height:0;border-top:2px solid red;border-right:2px solid red;animation:border-top-right 3s infinite alternate}@keyframes border-top-right{0%{width:0;height:0}25%{width:200px;height:0}50%{width:200px;height:48px}to{width:200px;height:48px}}.custom-button:after{content:"";position:absolute;right:0;bottom:0;width:0;height:0;border-bottom:2px solid red;border-left:2px solid red;animation:border-bottom-left 3s infinite alternate}@keyframes border-bottom-left{0%{width:0;height:0;opacity:0}50%{width:0;height:0;opacity:0}50.1%{width:0;height:0;opacity:1}75%{width:200px;height:0;opacity:1}to{width:200px;height:48px;opacity:1}}