Explain descendant selector in CSS with an example

Example: CSS descendant selectors

/*Descendant Selectors*/
/*Creates matching patterns based on the relationship between nested elements*/

<section>
	<a href="#"></a> -->/*to select "a" tag in CSS use */--> section a{...}   
</section>

/*Examples:*/
.class-selector-name 
.nested-class-name {...}

---tag with class="class-selector-name"
	|
	|--tag with class="nested-class-name"  <-- Selected

main h1 {...}

---main
	|--h1  <-- Selected
---h1 <-- Not selected!!!