It's a bit unclear what you're asking for in your question. If you want the font size to adjust based on the browser's viewport size, you can use vw units (check out the jsfiddle example below).
Take a look at this: http://jsfiddle.net/km1hbpzv/1/. Resize the browser window to see if that's the effect you're looking for.
I took the HTML and CSS code from your Pastebin post and made some modifications as per your original requirements.
Here are my changes:
#NewsPosts {
position: relative;
bottom: 0px;
top: -925px;
width: 45%;
text-align: center; /* changed from position: center */
font-size: 2vw; /* updated from 20px to 2vw (viewport width unit) */
}
#DateAndBy {
position: relative;
bottom: 0px;
top: -930px;
font-size: 3vw; /* updated from 30px to 3vw (viewport width unit) */
}
Your HTML structure may have some issues that could make future styling adjustments tricky, but for now, this should work based on the details provided in your post.
If you want to explore more about using vw units and other font-size practices, check out this link: Pure CSS to make font-size responsive based on dynamic amount of characters