*{ margin:0; padding:0; } html,body{ width:100%; height:100%; background:#040d32; } .border-box{ position: relative; margin:300px auto; width:400px; height:300px; background: rgba(1, 19, 67, 0.8); border: 2px solid #00a1ff; border-radius: 8px; } .border-box::before { position: absolute; top: -2px; bottom: -2px; left: 30px; width: calc(100% - 60px); content: ""; border-top: 2px solid #016886; border-bottom: 2px solid #016886; z-index: 0; } .border-box::after { position: absolute; top: 30px; right: -2px; left: -2px; height: calc(100% - 60px); content: ""; border-right: 2px solid #016886; border-left: 2px solid #016886; z-index: 0; }