/*background*/
html, body {
  font-family: 'MS UI Gothic';
  padding: 0;
  overflow: hidden;  
  position:relative;
  height: 100%;
  margin: 0;
  background-image: url(https://i.imgur.com/JYoeMM5.gif);
  animation: background 100s linear infinite;
}
@keyframes background {
    0% {
        background-position: 0%;
    }
    100% {
        background-position: 100% 100%;
    }
}

/*wrap: justifies content to center*/
.flex,
.flex-stack {
  display: flex;
  height: 100%;
  padding: 0;
  margin: 0;
  flex: 1;
  align-items: center;
  justify-content: center;
  flex-direction: column;
}

/*divs*/
.mainbox {
  background: linear-gradient(0deg, rgb(117, 119, 141) 20%, rgb(117, 127, 155) 60%);
  border: 3px dashed;
  border-color: #333faf;
  font-size: 18px;
  line-height: 1.2;
  
  width: 500px;
  height: fit-content;
  padding: 30px;
  flex-shrink: 0;
  display: flex;
  justify-content: center;
  border-radius: 50px;
}