Blogger's original instructions for expandable post summaries to the old Blogger template and Beta (now new Blogger / Blogger v.2) template is available here. However, that page is not without any faults and omissions like the other google.com pages, which are published in haste.
In Step 1: Conditional CSS (for layouts)
New Blogger templates or Layouts do not have a style-sheet by default. The styles are enclosed within the <b:skin></b:skin> tags. It is not possible to add the conditional <b:if cond='data:blog.pageType == "item"'><b:else/></b:if> tags within the skin tags. You have to add the conditional CSS within <style></style> tags outside the skin tags. Simply insert the following lines anywhere between the <head></head> tags.
<b:if cond='data:blog.pageType == "item"'>
Please note that using this hack will just reduce the amount of information that is displayed on the screen. The full content of the posts is still downloaded to the Web browser and available behind the screens (view page source) which means that there won't be any improvement in the download speed of the page. If you know of a hack that can help reduce the download speed of the index and archive pages by omitting the unwanted part of the posts from the page source, then please do hashout! » Continue reading