Introduction
What is happening there is your content is overflowing a pre-set height on the content boxes. You can limit these excerpts to a specific length by enabling excerpts in your post editor and copying a couple sentences into the field.
The Solution
To fix it with CSS, you can add the following style to the custom.css:
.sub-posts li {
height: auto;
}
This creates a varying height situation that isn’t very desireable to some people, which is why a specific height was chosen. If you prefer to keep that uniform style, add something suited to your content like 400px instead of “auto”. Adjust the height as needed.