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About the <head>

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CSS

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CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

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JavaScript

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Babel includes JSX processing.

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HTML 

              
                <fieldset id="gallery" class="hub">
  <div>
    <input type="radio" id="image-1" name="gallery" value="image-1" checked>
    <img src="https://assets.codepen.io/2585/image_fx_a_black_wolf_in_armor_wrecking_a_steampunk_ci.jpg" alt="" />
    <label for="image-1">Cyber Wolf</label>
  </div>

  <div>
    <input type="radio" id="image-2" name="gallery" value="image-2">
    <img src="https://assets.codepen.io/2585/image_fx_cyberpunk_city_scene_with_neon_streaks_of_lig+%283%29.jpg" alt="" />
    <label for="image-2">Flying cars</label>
  </div>

  <div>
    <input type="radio" id="image-3" name="gallery" value="image-3">
    <img src="https://assets.codepen.io/2585/image_fx_cyberpunk_city_scene_with_neon_streaks_of_lig+%282%29.jpg" alt="" />
    <label for="image-3">Flying cars 2</label>
  </div>
  
  <div>
    <input type="radio" id="image-4" name="gallery" value="image-4">
    <img src="https://assets.codepen.io/2585/image_fx_cyberpunk_city_scene_with_neon_streaks_of_lig+%281%29.jpg" alt="" />
    <label for="image-4">Flying cars 3</label>
  </div>
   
  <div>
    <input type="radio" id="image-5" name="gallery" value="image-5">
    <img src="https://assets.codepen.io/2585/image_fx_cyberpunk_city_scene_with_neon_streaks_of_lig+%284%29.jpg" alt="" />
    <label for="image-5">Cyber T-Rex</label>
  </div>
   
  <div>
    <input type="radio" id="image-6" name="gallery" value="image-6">
    <img src="https://assets.codepen.io/2585/image_fx_a_raptor_in_armor_wrecking_a_cyberbunk_city_w.jpg" alt="" />
    <label for="image-6">Cyber Raptor</label>
  </div>
   
  <div>
    <input type="radio" id="image-7" name="gallery" value="image-7">
    <img src="https://assets.codepen.io/2585/image_fx_cyberpunk_city_scene_with_neon_streaks_of_lig.jpg" alt="" />
    <label for="image-7">Cyber freeway</label>
  </div>
</fieldset>
!

CSS 

              
                @import "https://unpkg.com/open-props/easings.min.css";

@layer demo.view-transition {
  ::view-transition-group(*) {
    animation-duration: .5s;
    animation-timing-function: var(--ease-5);
  }
  
  .hub > * {
    @media (prefers-reduced-motion: no-preference) {
      &:nth-child(1) {
        view-transition-name: gallery-item-1;
      }
      &:nth-child(2) {
        view-transition-name: gallery-item-2;
      }
      &:nth-child(3) {
        view-transition-name: gallery-item-3;
      }
      &:nth-child(4) {
        view-transition-name: gallery-item-4;
      }
      &:nth-child(5) {
        view-transition-name: gallery-item-5;
      }
      &:nth-child(6) {
        view-transition-name: gallery-item-6;
      }
      &:nth-child(7) {
        view-transition-name: gallery-item-7;
      }
    }
}

@layer demo.layout {
  .hub {
    display: grid;
    gap: 1rem;
    grid-template-columns: repeat(5, 15vw);
    grid-template-rows: repeat(3, 15vw);
    
    &.portrait {
      grid-template-columns: repeat(3, 20vw);
      grid-template-rows: repeat(5, 20vw);
    }
    
    /* selected promotion */
    > :has(:checked) {
      grid-column: 1 / 4;
      grid-row: 1 / 4;
    }
    
    /* pile the label, input and image */
    > * {
      display: grid;
      
      > * {
        grid-area: 1/1;
      }
      
      > label {
        opacity: 0;
        cursor: pointer;
        -webkit-tap-highlight-color: transparent;
      }
      
      > input {
        border-radius: 0;
        outline-offset: 5px;
        outline-color: deeppink;
        outline-color: color(display-p3 1 0 1);
      } 
    }
  }
}

@layer demo.support {
  * {
    box-sizing: border-box;
    margin: 0;
  }

  html {
    block-size: 100%;
    color-scheme: dark light;
  }

  body {
    min-block-size: 100%;
    font-family: system-ui, sans-serif;

    display: grid;
    place-content: center;
  }
  
  fieldset {
    border: none;
    padding: 0;
    margin: 0;
  }
  
  img {
    max-inline-size: 100%;
  }
  
  html {
    view-transition-name: none;
  }
}
!

JS 

              
                // watch for radio group input clicks
// if VT is supported, prevent the default behavior
// call VT and manually set checked
document.querySelectorAll('#gallery input').forEach(radio => {
  radio.onclick = e => {
    if (!document.startViewTransition) return
    
    e.preventDefault()
    
    function mutate() {
      // radio group naturally handled unchecking the current one
      e.target.checked = true
      // reset the zindex so the next item can be on top
      e.target.parentNode.style.zIndex = null
    }
    
    // ensures selected item is on top during view transition
    e.target.parentNode.style.zIndex = 2
    
    // always mutate, but VT if possible
    document.startViewTransition
      ? document.startViewTransition(() => mutate())
      : mutate()
  }
})

// function to handle device rotation / page resize
function flipGallery() {
  function mutate(vertical = false) {
    if (document.startViewTransition)
      document.startViewTransition(() =>
        vertical
          ? gallery.classList.add('portrait')
          : gallery.classList.remove('portrait'))
  }
  
  mutate(window.innerWidth <= 768)
}

// throttled resize observer
// waits for 100ms of no resizing before firing flipGallery()
window.onresize = () => {
  clearTimeout(window.resizeEndTimer)
  window.resizeEndTimer = setTimeout(flipGallery, 100)
}
!
999px

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