Positioning some things in CSS is a bit of a nightmare.  However, aligning text is easy.

In textcss.html add these two paragraphs at the bottom (but before /body)

<p style="text-align:right; background-color:yellow;">Greetings from over here.</p>
<p style="text-align:center; background-color:yellow;">What are you doing over there?</p>

Note the spelling of center.  Save and view.

The default text alignment is left aligned. You should see from the yellow background that the paragraph does not move it is only the text which is aligned (within the paragraph). Remember that paragraphs are block elements and so by default will fill the width of the page (apart from their margins and page padding as explained later).