Check out example codes for "include css typo3". It will help you in understanding the concepts better.

Code Example 1

cssInline {
    10 = TEXT
    10.value = h1 {margin:15px;}

    20 = TEXT
    20.value = h1 span {color: blue;}

    30 = FILE
    30.file = EXT:mysite/Resources/Public/StyleSheets/styles.css
}

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