Details and Summary

The simplest example of details-summary is as was shown in the demonstation (Demo page) with only a bit of text for the summary and more text for details. The HTML code for producing that is merely:
<details>
<summary>Some topic of interest</summary>
<p class= "p1">Discussion of that interesting topic</p>
</details>
NOTE: .p1 has been styled to make this text red and to indent the text a few spaces.

Some topic of interest

Discussion of that interesting topic

Having an image in the details area is not much more complicated. The code follows:
&tldetails>
<summary>Where We Spend the Day</summary>
<p><img src= "schoolhouse.jpg"> In school, of course!</p>
</details>

Where We Spend the Day

In school, of course!