:root {
  --size: 6.4rem;
  --border: 1.2rem;
  --bg: black;
  --ringOutter: rgba(255, 255, 255, 0.2);
  --ringInner: rgba(20, 71, 230, 0.8);
}

html {
  box-sizing: border-box;
  font-size: 62.5%;
  scroll-behavior: smooth;
}

*,
*:before,
*:after {
  margin: 0;
  box-sizing: inherit;
}
body {
  height: 100dvh;
  width: 100vw;
  display: flex;
  justify-content: center;
  align-items: center;
  background-color: var(--bg);
}

.core {
  height: var(--size);
  width: var(--size);
  position: relative;
  border: var(--border) solid var(--ringOutter);
  border-radius: 50%;
  animation: spin 5s linear infinite forwards;

  &::after {
    content: "";
    height: var(--size);
    width: var(--size);
    position: absolute;
    top: 50%;
    left: 50%;
    background-image: linear-gradient(
      to bottom right,
      transparent 65%,
      var(--ringInner) 65%
    );
    border-radius: 50%;
    transform: translate(-50%, -50%);
  }

  &::before {
    content: "";
    height: calc(var(--size) - var(--border));
    width: calc(var(--size) - var(--border));
    position: absolute;
    top: 50%;
    left: 50%;
    background-color: var(--bg);
    border-radius: 50%;
    z-index: 5;
    transform: translate(-50%, -50%);
  }
}

@keyframes spin {
  0% {
    opacity: 1;
    transform: rotate(0deg);
  }
  50% {
    opacity: 0.2;
  }
  100% {
    opacity: 1;
    transform: rotate(360deg);
  }
}