I don’t know why the theme developer did this, but he/she added the following rule to the CSS file:
ol li {
display: inline-block;
}
This rule is making all of the list items for an ordered list appear on a single line. This rule, in my opinion, is overly broad. There are many instances in which list items are made inline (in menus, for example), but in those cases, a class selector should be used so the rule doesn’t affect every single use of ordered lists by default.
So, what you can do is add this CSS rule:
ol li {
display: block;
}
You shouldn’t edit the theme’s stylesheet directly (unless it’s a custom theme made for your site), but use a CSS plugin like Custom CSS Manager.