CSS: “padding-bottom”: X negative values are not allowed.

A padding-bottom declaration has a negative value, and padding can't be less than zero.

Bottom padding is the space between the bottom of an element's content and its bottom border, so CSS only accepts zero or a positive length or percentage for it. A browser drops a padding-bottom declaration with a negative value, and the element keeps whatever bottom padding it gets from other rules. Adding !important doesn't change that: the declaration is still invalid, and the validator still reports it.

A negative bottom padding is usually an attempt to pull the next element up, or to make it overlap the bottom of this one. A negative margin-bottom does that, and CSS allows it. To fix the error, set padding-bottom to 0 or a positive length, and move the negative value to margin-bottom if you still need the overlap. The padding shorthand and the other side properties follow the same rule, and each one has its own message.

Invalid example

<div class="banner" style="padding-bottom: -20px;">
  Banner content
</div>
<p>The next paragraph starts here.</p>

Valid example

<div class="banner" style="padding-bottom: 0; margin-bottom: -20px;">
  Banner content
</div>
<p>The next paragraph starts here.</p>

Learn more:

MDN Reference

MDN Web Docs: padding-bottom

→

MDN Reference

MDN Web Docs: margin-bottom

→