Image lightboxes with 'show me the alt text' buttons... in pure CSS

[Dan Q]

I had an idea recently and wanted to share it: a way of making:

• "Lightboxes" (images where when you click them, you see a bigger/higher-def version as a "popover"/"overlay"),
• with a "show alt text" button like Mastodon has (because alt text is for everybody!),
• in pure CSS and semantic HTML (no JS = fast performance, less to break!)

Here's what I came up with! The short of it is that you have some HTML code like this:

Code: html

<figure>
  <div class="img-with-alt-text">
    <details class="lightbox">
      <summary>
        <img src="owls-thumbnail.jpg" width="640" height="400" alt="A pair of barred owls rest in the shade of a leafy deciduous tree in the afternoon light.">
      </summary>
      <span class="lightbox-full-image">
        <img src="owls-full.jpg" width="6016" height="4016" loading="lazy" alt="Large image of a pair of barred owls rest in the shade of a leafy deciduous tree in the afternoon light.">
      </span>
    </details>
    <details class="alt-text">
      <summary><span>Alt</span></summary>
      <p>A pair of barred owls rest in the shade of a leafy deciduous tree in the afternoon light.</p>
    </details>
  </div>
  <figcaption>
    Photo courtesy Tom Nebel, used under the Pexels license.
  </figcaption>
</figure>

This works by itself because of the semantic HTML, but it's not very pretty, so we enhance it with this CSS:

Code: css

body:has(.lightbox[open]) {
  overflow: hidden;
}

figure {
  width: fit-content;
}

.img-with-alt-text {
  position: relative;
}

.lightbox {
  display: inline-block;
  width: fit-content;
  margin: 0 auto;

  summary {
    list-style: none;
    cursor: zoom-in;
  }

  &[open] {
    summary {
      cursor: zoom-out;

      &::after {
        content: "";
        position: fixed;
        z-index: 1;
        background-color: rgba(0, 0, 0, 0.6);
        backdrop-filter: blur(2px);
        inset: 0;
      }
    }

    .lightbox-full-image {
      position: fixed;
      inset: 0;
      z-index: 2;
      pointer-events: none;
      display: flex;
      justify-content: center;
      align-items: center;
      padding: 1.5ch;

      img {
        object-fit: contain;
        z-index: 3;
        height: 100%;
        width: 100%;
      }
    }
  }
}

.alt-text {
  font-size: 90%;

  summary, p {
    background: rgba(0, 0, 0, 0.65);
    color: var(--color-secondary);
    border-radius: 4px;
    padding: 1px 3px;
    margin: 0;
  }

  summary {
    position: absolute;
    bottom: 10px;
    left: 5px;
    list-style: none;
    cursor: pointer;
    text-transform: uppercase;
  }

  p {
    right: 5px;
  }

  &[open] {
    position: absolute;
    bottom: 10px;
    left: 5px;
    right: 5px;

    summary {
      position: absolute;
      top: 0;
      left: 0;
      right: 0;
      bottom: 0;
      background: transparent;

      span {
        display: none;
      }

      p {
        right: 5px;
        margin: 0;
        padding: 0 2px;
      }
    }
  }
}

I don't like the repetition in the HTML, but if you're using a CMS or a Static Site Generator then it's unlikely to be an issue.

Anyway, have a play with what I came up with if it's the kind of thing that interests you. Could be great for a blog or a gallery page.