A solution that most people use is adding a SPAN tag to the list item and style the OL tag first and re-style the SPAN tag.
CSS
ol { font-weight: bold }
ol span { font-weight: normal }
HTML
<ol>
<li><span>Item 1</span></li>
<li><span>Item 2</span></li>
<li><span>Item 3</span></li>
<li><span>Item 4</span></li>
<li><span>Item 5</span></li>
</ol>
But there is another way with only CSS2 stylesheet.
ol { counter-reset: item }
ol li { display: block }
ol li:before {
content: counter(item) ". ";
counter-increment: item;
font-weight: bold;
}
Result of a ordered list without span tags and the above CSS:
- Item 1
- Item 2
- Item 3
- Item 4
- Item 5
For some more info check w3schools.com page: CSS counter-increment property