Indentation is a method for making code readable when it is nested. It is not a method to make code nested.
Here is some nested code that is not indented and is harder to read:
<main>
<p>I am nested in main</p>
<h2>so am I </h2>
</main>
Here is code that has no nesting.
<p>this is the first sibling</p>
<p>this is the second </p>
<h3>this is the third</h3>
Notice how in the nested example, the opening tag for main was before the other lines of code while it’s closing tag was included after the enclosed lines were completed? This is nesting.