问题:

I have set the list-style-type in CSS, but for some reason it's not showing it.

body {
  margin: 0;
}
ol {
  list-style-type: decimal;
  padding-left: 0;
}

<ol>
  <li>Item 1</li>
  <li>Item 2</li>
  <li>Item 3</li>
</ol>

回答1:

Because of your padding reset, the numbers are actually off to the left of the page. Try adding:

list-style-position: inside;

回答2:

display:list-item;
list-style-position:outside;

It may give problem if list display: attribute is set to some thing else than display:list-item;

回答3:

Decimal is default for an "ol". No need to declare it. Also the numbers are there just falling off the side of the page i.e. invisible. Adjust your padding and get rid of the redundant declaration. See here

回答4:

If nothing of this work, make sure you don't have elements explicitly marked as display block inside the LI. It just happened to me with a H4 A set as block inside the LI. I was about to resign