Custom background colour to only one sentence within a text block

Hi forum,

Quick question.

I'm trying to emphasise a key sentence within a larger body of text in a text block by changing the background and text colour of only that sentence. 

Essentially, I want what it looks like when you change the background and text colour in a rich text editor, like this:

First sentence. *Key Sentence.* Third sentence.

Any help would be very much appreciated.

You can bold/underline/list... that text (It will has different tag compared to the rest of the text at that time), then use CSS to set background, color, size... for only that tag.