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This was a specific example; however the tutorial applies to every element type you can choose to edit. Once you mouse over the element with the inspector selector, you have to determine the correct lines of code to modify by carefully reading through the CSS identifier lines (because some elements have different states, like this Create button had a hover state). The lines of CSS that are striked-through usually indicate lines that are old and have been previously changed for elements that don't have different states. 

Once you have the correct lines of CSS identified you can edit the element as much as you'd like using CSS commands.