.box{ position: relative; width: 300px; height: 450px; display: flex; justify-content: center; align-content: center; background: #060c21; padding:10px} 
.box::before{ content: ''; position: absolute; top: -2px; bottom: -2px; left: -2px; right: -2px; background: #fff; z-index: -1;}
.box::after{ content: ''; position: absolute; top: -2px; bottom: -2px; left: -2px; right: -2px; background: #fff; z-index: -1; filter: blur(40px);}
.box::before, .box::after{ background: linear-gradient(235deg, #ffff, #060c21, #00bcd4);}

/*.box{ position: relative; width: 300px; height: 450px; display: flex; justify-content: center; align-content: center; background: transparent; padding:10px} 
.box::before{ content: ''; position: absolute; top: -2px; bottom: -2px; left: -2px; right: -2px; background: transparent; z-index: -1;}
.box::after{ content: ''; position: absolute; top: -2px; bottom: -2px; left: -2px; right: -2px; background: transparent; z-index: -1; filter: blur(40px);}
.box::before, .box::after{ background: linear-gradient(235deg, transparent, transparent, transparent);}*/