style.css

*{
   margin: 0;
   padding: 0;
   box-sizing: border-box;
   
}
body{
   background-color: rgb(3, 3, 34);
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
}

.container{
   width: 400px;
   height: 400px;
   text-align: center;
   background-color: hsl(245, 95%, 48%);
   color: #fff;
   border-radius:5px ;
   position: relative; 
   display: flex;
   justify-content: center;
   align-items: center;
}

.elemento-text{
   margin: 1rem;
   align-items: center;
}

.container .elemento-text h1{
   font-size: 30pt;
}

.container .elemento-text p{
   font-size: 15pt;
   padding: .5rem;
}

.container::before, .container::after{
   content: " ";
   position: absolute;
   z-index: -1;
   width: calc(100% + 30px);
   height: calc(100% + 30px);
   background: linear-gradient(45deg, #eaff00,rgb(21, 0, 251),rgb(255, 0, 0),#eaff00,rgb(255, 0, 0),rgb(21, 0, 251),rgb(255, 0, 0),#eaff00,rgb(0, 0, 255));
   background-size: 300%;
   border-radius: 8px;
   animation: animarBorda 10s linear alternate infinite;
}

@keyframes animarBorda{
   0%{
     background-position: 0%;
   }
   100%{
     background-position: 300%;
   }
}

.container::after{
   filter: blur(50px);
}