Why Does 'top: 50%' Not Center Elements Correctly in Responsive Layouts?

Why is CSS "top: 50%" Not Working as Expected in Responsive Layouts?

In responsive web design, using percentages for CSS properties like "top" is crucial for maintaining element positioning across different screen sizes. However, issues can arise when "top: 50%" doesn't align elements correctly.

Consider the following HTML and CSS code:

<div>
<p>The issue here is that the "top" property for the child div references the height of the parent div, which is undefined. As a result, the child div won't be positioned at 50% from the top of the viewport.</p>
<p>To solve this, you must define a specific height for the parent div. For example:</p>
<pre class="brush:php;toolbar:false"><div>
<p>Now, the child div will be positioned at 50% from the top of the parent div, which has a defined height.</p>
<p>Alternatively, you can stretch the parent div to fill the entire viewport by setting its "top," "bottom," "left," and "right" properties:</p>
<pre class="brush:php;toolbar:false"><div><p>By defining the parent div's dimensions or stretching it to fill the viewport, you ensure that percentages like "top: 50%" can align elements correctly in responsive layouts.</p></div>