伪元素 "content"属性中的 CSS 变量(自定义属性)

Question

使用示例(我想要的)

div::after {
  content: var(--mouse-x) ' / ' var(--mouse-y);
}

测试用例显示它不工作:

CodePen: CSS Variables in Pseudo Element's "content:" Property (a test case) by Jase Smith

document.addEventListener('mousemove', (e) => {
  document.documentElement.style.setProperty('--mouse-x', e.clientX)
  document.documentElement.style.setProperty('--mouse-y', e.clientY)
  
  // output for explanation text
  document.querySelector('.x').innerHTML = e.clientX
  document.querySelector('.y').innerHTML = e.clientY
})

/* what I want!! */
div::after {
  content: var(--mouse-x, 245)" / " var(--mouse-y, 327);
}

/* setup and presentation styles */
div::before {
  content: 'mouse position:';
}
div {
  position: absolute;
  top: 0;
  left: 0;
  transform: translate(calc(var(--mouse-x, 245) * 1px), calc(var(--mouse-y, 327) * 1px));
  width: 10em;
  height: 10em;
  background: #ff3b80;
  color: #fff;
  display: flex;
  flex-flow: column;
  align-items: center;
  justify-content: center;
  border-radius: 100%;
  will-change: transform;
}
body {
  margin: 2em;
  font-family: sans-serif;
}
p {
  max-width: 50%;
  min-width: 25em;
}

<!-- test case: element with pseudo element -->
<div></div>

<!-- explanation (not test case) -->
<main>
  <pre><code>div::after {
  content: var(--mouse-x) ' / ' var(--mouse-y);
}</code></pre>
  <h1>If this worked...</h1>
  <p>
    We should see something like this: <b><span class="x">245</span> / <span class="y">327</span></b> updating with the mousemove coordinates inside the pseudo <i>::after</i> element for the div.
  </p>
</main>

Answer 1

为清楚起见进行编辑:具有整数值的 CSS 自定义属性可以通过 CSS counter 显示在伪元素的 content 属性中。 .

div {
    --variable: 123;
}
span:after {
    counter-reset: variable var(--variable);
    content: counter(variable);
}

<div>The variable is <span></span>.</div>

.coordinates:before {
    counter-reset: x var(--x) y var(--y);
    content: 'The coordinates are (' counter(x) ', ' counter(y) ').';
}

<div class="coordinates" style="--x: 1; --y: 2"></div>

---

原始答案

使用涉及 CSS Counters 的黑客让它工作.享受吧。

div::after {
  counter-reset: mouse-x var(--mouse-x, 245) mouse-y var(--mouse-y, 245);
  content: counter(mouse-x) " / " counter(mouse-y);
}

完整代码:

document.addEventListener('mousemove', (e) => {
  document.documentElement.style.setProperty('--mouse-x', e.clientX)
  document.documentElement.style.setProperty('--mouse-y', e.clientY)
  
  // output for explanation text
  document.querySelector('.x').innerHTML = e.clientX
  document.querySelector('.y').innerHTML = e.clientY
})

/* what I want!! */
div::after {
  counter-reset: mouse-x var(--mouse-x, 245) mouse-y var(--mouse-y, 245);
  content: counter(mouse-x) " / " counter(mouse-y);
}

/* setup and presentation styles */
div::before {
  content: 'mouse position:';
}
div {
  position: absolute;
  top: 0;
  left: 0;
  transform: translate(calc(var(--mouse-x, 245) * 1px), calc(var(--mouse-y, 327) * 1px));
  width: 10em;
  height: 10em;
  background: #ff3b80;
  color: #fff;
  display: flex;
  flex-flow: column;
  align-items: center;
  justify-content: center;
  border-radius: 100%;
  will-change: transform;
}
body {
  margin: 2em;
  font-family: sans-serif;
}
p {
  max-width: 50%;
  min-width: 25em;
}

<!-- test case: element with pseudo element -->
<div></div>

<!-- explanation (not test case) -->
<main>
  <pre><code>div::after {
  content: var(--mouse-x) ' / ' var(--mouse-y);
}</code></pre>
  <h1>If this worked...</h1>
  <p>
    We should see something like this: <b><span class="x">245</span> / <span class="y">327</span></b> updating with the mousemove coordinates inside the pseudo <i>::after</i> element for the div.
  </p>
</main>