This is possible in three ways, one way is to add a class to item that you want to edit. In this case to 3rd item, second way is through custom CSS and third way is through style attribute.
Option 1: Through class
If you click to edit 3rd item and add class “card-highlight” for example, only that item will have that class. Which means now whatever style is coming from that class, it will be applied to only that item in loop.
But be aware: tag styles are stronger than class styles.
What this means is, if you have background style applied to tag, whatever is coming from class will not override tag styles, one trick to override it is to open custom CSS and add !important in class styles.
For example: background:blue!important;
Option 2: Through style attribute
You can change attribute of specific tag inside of loop without affecting any other tag. This means you can add style attribute and change styles only of selected tag.
You can see on example below that I changed background color only of 2nd item in loop.
This is the hardest way, for some people might be overwhelming, but developers will like this way of doing things.
If you click on looped item (parent), then you can open custom CSS tab and target specific elements with :nth-child feature of CSS. For example you can edit every 2nd looped item using :nth-child(odd) or you can style heading 3 inside of 2nd loop item by using :nth-child(2) h3.
You can see the idea in the screenshot below.
If you would like to learn more about nth child possibilites, you can do it here.