custom-file-tree/dist/file-tree.css

Add the custom element to your page context using plain old HTML:

.drag-and-drop-hidden {
  display: none !important;
  opacity: 0;
}

file-tree {
  --fallback-icon: "🌲";
  --open-dir-icon: "📒";
  --closed-dir-icon: "📕";
  --file-icon: "📄";

  --dir-touch-padding: 0;
  --open-dir-icon-cursor: pointer;
  --closed-dir-icon-cursor: pointer;
  --dir-heading-cursor: pointer;
  --file-icon-cursor: pointer;
  --file-heading-cursor: pointer;

  --icon-size: 1.25em;
  --line-height: 1.5em;
  --indent: 1em;
  --entry-padding: 0.25em;

  --highlight-background: lightcyan;
  --highlight-background-bw: #ddd;
  --highlight-border-color: blue;
  --drop-target-color: rgb(205, 255, 242);

  position: relative;

  &:not([show-top-level]) {
    padding-top: 0;
    padding-left: 0;
    dir-entry[path="."] {
      & > span.icon,
      & > entry-heading {
        display: none;
      }
      & > .buttons {
        width: calc(100% + 0.5em);
        background: var(--highlight-background-bw);
        text-align: center;
        border-bottom: 1px solid black;
      }
    }
  }

  /* All entries in the file tree have a handy icon */

  .icon {
    position: relative;
    display: inline-block;
    width: var(--icon-size);
    height: var(--icon-size);
    cursor: pointer;
    &:before {
      position: absolute;
      bottom: -0.25em;
      left: 0;
      content: var(--fallback-icon);
    }
  }

  /* The root dir has an icon, but it's "inactive" */

  [path="."] > .icon {
    cursor: default !important;
  }

  /*
    And the file tree  technically has an icon and even a
    heading, but they're both "dummy" nodes.
  */

  & > .icon {
    display: none !important;
  }

  & > entry-heading {
    display: none !important;
  }

  /*
    The root buttons should always be visible, but entry
    buttons should only be revealed when the associated
    entry has been selected by the user.
  */

  & .buttons {
    display: none;
    height: var(--line-height);
  }

  & .selected > .buttons,
  & [path="."] > .buttons {
    display: inline-block;
  }

  /* Headings are clickable */

  entry-heading {
    cursor: pointer;
    display: inline-block;
  }

  [path="."] > entry-heading {
    cursor: default;
  }

  .selected {
    & > entry-heading {
      background: var(--highlight-background);
      border: 1px solid var(--highlight-border-color);
      margin-top: -1px;
      margin-bottom: -1px;
      padding-left: var(--entry-padding);
      padding-right: var(--entry-padding);
    }
    & .buttons {
      max-height: 1em;
    }
  }

  /* Drag and drop has its own visual cues */

  .dragging {
    opacity: 0.2;
  }
  .drop-target {
    background: var(--drop-target-color);
  }

  /* Directories */

  dir-entry {
    display: block;
    min-height: var(--line-height);
    margin-left: var(--indent);

    /* Note: the root dir does not get indented */

    &[path="."] {
      margin-left: 0;
    }

    & > .icon {
      cursor: var(--open-dir-icon-cursor);
      &:before {
        content: var(--open-dir-icon);
      }
    }

    & > entry-heading {
      cursor: var(--dir-heading-cursor);
      /*
        It's super easy to mistouch dirs, so we give them a little more space
      */
      padding-top: var(--dir-touch-padding);
      padding-bottom: var(--dir-touch-padding);
    }

    &.closed {
      & > file-entry,
      & > dir-entry {
        display: none;
      }

      & > .icon {
        cursor: var(--closed-dir-icon-cursor);
        &:before {
          content: var(--closed-dir-icon);
        }
      }
    }

    /* Files */

    file-entry {
      display: block;
      margin-left: var(--indent);
      height: var(--line-height);

      & > .icon {
        cursor: var(--file-icon-cursor);
        &:before {
          content: var(--file-icon);
        }
      }

      & > entry-heading {
        cursor: var(--file-heading-cursor);
      }
    }
  }
}

/*
  for touch devices, we want to make sure that our fat fingers can still click drag  entries
*/
@media (pointer: coarse) {
  file-tree {
    --dir-touch-padding: 0.4em;
  }
}