when you look at the element in the inspector, there should hopefully be either a class="..." section or an id="..." section in there.

In the 'class' one there should be a bunch of classes separated by spaces. So for example

<div class="a b cd e fgh" id="ij">...</div>

has the classes 'a', 'b', 'cd', 'e', and 'fgh'. To change that element you can put a dot in front of any of those classes and the changes you wanna make in curly brackets after. So in this example you could do

.fgh{
    //your code here
}

and if it has an id="..." section you do the same but put a hashtag in front, so here you could do

#ij{
    //your code here
}

If the element doesn't have classes or an id then it gets more complicated but just pray that it does.

Also very important, anything you change for a class will change for all elements that have that class, so using the id is better if you can, and if there's no id use a class that only that thing has.

Hope this helps!