Text enlargement and separator line unexpectedly appear in markdown

[gusah009]

What happened:

When arranging the markdown in the given format, the text unexpectedly enlarges and a separator line appears below the section.

What you expected to happen:

The text should remain the same size without any additional features such as a separator line.

How to reproduce it (as minimally and precisely as possible):

Follow the markdown layout provided in the image link:

Anything else we need to know?:

Environment:

• Operating system: Not specified
• Browser and version: Not specified
• CodePair version: Not specified