discourse/app/assets/stylesheets/common/loading-slider.scss

.loading-indicator-container {
  --loading-width: 0.8;
  --still-loading-width: 0.9;

  --still-loading-duration: 10s;
  --done-duration: 0.4s;
  --fade-out-duration: 0.4s;

  position: fixed;
  top: 0;
  left: 0;
  z-index: z("header") + 1;

  height: 3px;
  width: 100%;

  opacity: 0;
  transition: opacity var(--fade-out-duration) ease var(--done-duration);

  background-color: var(--primary-low);

  .loading-indicator {
    height: 100%;
    width: 100%;
    transform: scaleX(0);
    transform-origin: left;
    background-color: var(--tertiary);
  }

  &.loading,
  &.still-loading {
    opacity: 1;
    transition: opacity 0s;
  }

  &.loading .loading-indicator {
    transition: transform var(--loading-duration) ease-in;
    transform: scaleX(var(--loading-width));
  }

  &.still-loading .loading-indicator {
    transition: transform var(--still-loading-duration) linear;
    transform: scaleX(var(--still-loading-width));
  }

  &.done .loading-indicator {
    transition: transform var(--done-duration) ease-out;
    transform: scaleX(1);
  }

  &.discourse-hub-webview {
    // DiscourseHub obscures the top 1px to work around an iOS bug
    top: 1px;
  }

  body.footer-nav-ipad & {
    top: var(--footer-nav-height);
  }
}

.loading-slider-fallback-spinner {
  padding-top: 1.8em;
  display: none;
}

body.still-loading {
  .loading-slider-fallback-spinner {
    display: block;
  }

  #main-outlet {
    display: none;
  }
}