.bg-glow-lines-right {
  display: block;
  position: absolute;
  border-radius: 2px;
  height: 1px;
  width: var(--size);
  background: linear-gradient(
    to left,
    #9d9bf2 0.43%,
    #7877c6 14.11%,
    rgba(120, 119, 198, 0) 62.95%
  );
}

.bg-glow-lines-down {
  display: block;
  position: absolute;
  border-radius: 2px;
  top: 0;
  right: 0;
  height: var(--size);
  width: 1px;
  background: linear-gradient(
    to top,
    #9d9bf2 0.43%,
    #7877c6 14.11%,
    rgba(120, 119, 198, 0) 62.95%
  );
}

.glow-container {
  position: absolute;
  top: -1px;
  left: 0;
  z-index: 0;
  height: 100%;
  width: calc(100% + 1px);
}

@keyframes line-right {
  0% {
    opacity: 0;
    left: -10%;
  }
  20% {
    opacity: 1;
  }

  100% {
    opacity: 0;
    left: var(--length);
  }
}

@keyframes line-down {
  0% {
    opacity: 0;
    top: 0px;
  }
  20% {
    opacity: 1;
  }

  100% {
    opacity: 0;
    top: var(--length);
  }
}

.glow-animation-right {
  animation-name: line-right;
  animation-duration: var(--duration);
  animation-iteration-count: 1;
  animation-timing-function: ease-out;
  animation-fill-mode: forwards;
}
.glow-animation-down {
  animation-name: line-down;
  animation-duration: var(--duration);
  animation-iteration-count: 1;
  animation-timing-function: ease-out;
  animation-fill-mode: forwards;
}

.box {
  position: relative;
  width: 500px;
  height: 300px;
  background: #fafafa;
  margin: 100px;
}