html - Toggle radio input using CSS only

Question

The following code use a script to toggle/uncheck a radio when clicked a second time on the same.

My question is how do I do this using CSS only?

(function(lastimg) {
  document.querySelector("#img-select").addEventListener('click', function(e){
    if (e.target.tagName.toLowerCase() == 'input') {
      if (lastimg == e.target) {
        e.target.checked = false;
        lastimg = null;
      } else {
        lastimg = e.target;
      }      
    }
  });
}());

.container {
  display: flex;
  flex-wrap: wrap;
  max-width: 660px;
}
.container > label {
  flex: 1;
  flex-basis: 33.333%;
}
.container > div {
  flex: 1;
  flex-basis: 100%;
}
.container label img {
  display: block;
  margin: 0 auto;
}
.container input, .container input ~ div {
  display: none;
  padding: 10px;
}

.container #img1:checked ~ #img1txt,
.container #img2:checked ~ #img2txt,
.container #img3:checked ~ #img3txt,
.container #img4:checked ~ #img4txt {
  display: block;
}

<div id="img-select" class="container">
  <input id="img1" type="radio" name="img-descr">
  <input id="img2" type="radio" name="img-descr">
  <input id="img3" type="radio" name="img-descr">

  <label for="img1">
    <img src="http://lorempixel.com/200/200/food/1/" alt="">
  </label>
  <label for="img2">
    <img src="http://lorempixel.com/200/200/food/6/" alt="">
  </label>
  <label for="img3">
    <img src="http://lorempixel.com/200/200/food/8/" alt="">
  </label>

  <div id="img1txt">
    <div>Recipe nr 1</div>
  </div>
  <div id="img2txt">
    <div>Recipe nr 2</div>
  </div>
  <div id="img3txt">
    <div>Recipe nr 3</div>
  </div>
</div>

Answer 1

You can't change the functionality of radio buttons using CSS. CSS is designed for visual changes only.

That said, you can simulate this behavior with a clever hack. For your example, I'd recommend using CSS to visually replace the label for the currently selected radio button with a dummy label attached to another radio button representing a "blank" or "empty" selection. That way, clicking the dummy label would select the "blank" option, effectively clearing your prior choice:

.container {
  display: flex;
  flex-wrap: wrap;
  max-width: 660px;
}
.container > label {
  flex: 1;
  flex-basis: 33.333%;
}
.container > div {
  flex: 1;
  flex-basis: 100%;
}
.container label img {
  display: block;
  margin: 0 auto;
}
.container input, .container input ~ div {
  display: none;
  padding: 10px;
}

.container #img1:checked ~ #img1txt,
.container #img2:checked ~ #img2txt,
.container #img3:checked ~ #img3txt {
  display: block;
}

.container label[for=noimg] {
  display: none;
}

.container #img1:checked ~ label[for=img1],
.container #img2:checked ~ label[for=img2],
.container #img3:checked ~ label[for=img3] {
  display: none;
}

.container #img1:checked ~ label[for=img1] + label[for=noimg],
.container #img2:checked ~ label[for=img2] + label[for=noimg],
.container #img3:checked ~ label[for=img3] + label[for=noimg] {
  display: block;
}

<div id="img-select" class="container">
  <input id="noimg" type="radio" name="img-descr">
  <input id="img1" type="radio" name="img-descr">
  <input id="img2" type="radio" name="img-descr">
  <input id="img3" type="radio" name="img-descr">

  <label for="img1">
    <img src="http://lorempixel.com/200/200/food/1/" alt="">
  </label>
  <label for="noimg">
    <img src="http://lorempixel.com/200/200/food/1/" alt="">
  </label>
  <label for="img2">
    <img src="http://lorempixel.com/200/200/food/6/" alt="">
  </label>
  <label for="noimg">
    <img src="http://lorempixel.com/200/200/food/6/" alt="">
  </label>
  <label for="img3">
    <img src="http://lorempixel.com/200/200/food/8/" alt="">
  </label>
  <label for="noimg">
    <img src="http://lorempixel.com/200/200/food/8/" alt="">
  </label>

  <div id="img1txt">
    <div>Recipe nr 1</div>
  </div>
  <div id="img2txt">
    <div>Recipe nr 2</div>
  </div>
  <div id="img3txt">
    <div>Recipe nr 3</div>
  </div>
</div>