How does CSS set the browser text to be smaller than 12px

How does CSS set the browser text to be smaller than 12px

Use transform: scaleto zoom

transform: scale(0.8);

<div>
	<p class="first">第一段文字</p>
	<p class="second">第二段文字</p>
</div>

.first {
    
    
	font-size: 12px;
}

.second {
    
    
	font-size: 12px;
	transform: scale(0.8);
}