The purpose of a hierarchy is to visual separate contents which may otherwise be confusing.

If there are main topics, then several sub-areas under each topic a visual hierarchy assists the user in distinguishing different topics quickly, then being able to "tunnel down" to more specific subjects related to that main topic.

However, if there are no sub-categories and there are only main topics, any visual hierarchy may lead a user to think some topics are more important than others, when they are not.

Given the simple list of 4 topics, there is no need for any visual hierarchy beyond the order the topics are stacked. I would remove all indents and nesting. They are entirely unwarranted in my opinion.

Simple, clean, clear.

The purpose of a hierarchy is to visual separate contents which may otherwise be confusing.

If there are main topics, then several sub-areas under each topic a visual hierarchy assists the user in distinguishing different topics quickly, then being able to "tunnel down" to more specific subjects related to that main topic.

However, if there are no sub-categories and there are only main topics, any visual hierarchy may lead a user to think some topics are more important than others, when they are not.

Given the simple list of 4 topics, there is no need for any visual hierarchy beyond the order the topics are stacked. I would remove all indents and nesting. They are entirely unwarranted in my opinion.

Simple, clean, clear.

Additional...

If you were to have sub topics, an easy way to handle it for the web/mobile is via expanding divs with an indicator that the topic expands....

Essentially it all boils down to a menu or navigation tree. That's all a TOC really is. So don't do anything in a TOC that you wouldn't do in a menu.

The purpose of a hierarchy is to visual separate contents which may otherwise be confusing.

If there are main topics, then several sub-areas under each topic a visual hierarchy assists the user in distinguishing different topics quickly, then being able to "tunnel down" to more specific subjects related to that main topic.

However, if there are no sun-categories and there are only main topics, any visual hierarchy may lead a user to think some topics are more important than others, when they are not.

Given the simple list of 4 topics, there is no need for any visual hierarchy beyond the order the topics are stacked. I would remove all indents and nesting. They are entirely unwarranted in my opinion.

Simple, clean, clear.

The purpose of a hierarchy is to visual separate contents which may otherwise be confusing.

If there are main topics, then several sub-areas under each topic a visual hierarchy assists the user in distinguishing different topics quickly, then being able to "tunnel down" to more specific subjects related to that main topic.

However, if there are no sub-categories and there are only main topics, any visual hierarchy may lead a user to think some topics are more important than others, when they are not.

Given the simple list of 4 topics, there is no need for any visual hierarchy beyond the order the topics are stacked. I would remove all indents and nesting. They are entirely unwarranted in my opinion.

Simple, clean, clear.