How do I alter line spacing in a single block (without affecting all pages)?

I'm not familiar with CSS but would like to have reduced line spacing in a single text block. I'm sure there's a simple CSS command for this. Any help would be much appreciated!

'Option + click' or 'alt + click' (I think) to bring up that block's code editing window. Depending on how your text is defined in the HTML, you could do something like this:

<p style="line-height: 1.1;">This is the text in your text block.</p>

or

<span style="line-height: 1.1;">This is the text in your text block.</span>

Basically the CSS property 'line-height' is what you want to focus on. Does this help?

You can do this pressing "Shift"+"Enter" and that will create a single line space instead of double