How to select the child element of the first specific class name without fixed number of elements?

Precise positioning: How to select the element of the first specific class name among the child elements with an uncertain number?

In web development, we often encounter situations where we need to select the first element with a specific class name among the uncertain number of child elements. For example, in a dynamically generated HTML structure, the number of child elements may change at any time. Suppose we have the following HTML structure:

<div class="main">
  <div class="activebar"></div>
  <div class="activebar"></div>
  <div class="activebar"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
</div>

The number of activebar and item elements is dynamically changed, we need to use CSS to select the first item class element. Neither item:first-child nor :first-of-type can meet this requirement, because they only select the first child element of the parent element and the first specific type of element, respectively.

The solution is to cleverly use CSS's :nth-child pseudo-class selector. We can use the following CSS code:

 .main .item:nth-child(n 1 of .item) {
  /* Style definition*/
}

The meaning of this code is: under the .main element, select the first .item element. nth-child(n 1 of .item) means counting from the first .item element and selecting the first matching element.

Through this method, we successfully solved the problem of accurately selecting the first specific class name element when the number of child elements is not fixed. The power of :nth-child selector provides a flexible solution for us to handle dynamic web elements.

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