how to add extra vertical space after a tag

This is my <style> block:

<style>
 p {text-align:left; font-size:10pt; font-family:Arial,sans-serif; line-height:1.2em;}
 br.big {display:block; content:""; margin-top:0.5em; line-height:190%; vertical-align:top;}
 p.big {margin-top:1.5em}
</style>

I'm showing the tags in red. 
 
This page illustrates ways of adding variable amounts of extra vertical space after a “ ” line break (or between paragraphs). 

This line ends in a plain “ ” tag. 
This next line ends in “ ” (the effect is identical). 
This line is sufficiently long that it exceeds 40em (the max-width), so that it will wrap and occupy two lines on the screen. 
This line ends has a bit of extra space after it, via the “vertical-align:-37%” trick.  
You don't need to use “ ” because all other space characters also work, including regular space, thin space ( ), hair space ( ), zero-width space (), and zero-wdith no-break space (BOM = U+FEFF = = ). 
In fact, to my surprise, it even works with no space at all (but I don't recommend this, because it's surprising, and because an HTML optimizer might remove it): 
This line demonstrates it. 
37% looks nice, but there's nothing magical about it. This line uses 75% for more vertical space.  
This line uses 25% for a smaller gap.  
This is the last line of the paragraph, which is intentionally very long, so that it will exceed the max-width and wrap onto more than one line on the screen, so that you can see the spacing difference.

This is a new paragraph, beginning with  and ending with .

This is another new paragraph, beginning with  and ending with .

This is a new paragraph, beginning with  so that it will have a bit of extra space before the first line.

In this paragraph, the first line is intentionally very long, so that it will exceed 40em (the max-width) and wrap onto more than one line on the screen, so that you can see the default line-spacing. 
This is a short line. 
This is another short line, but with extra space after it. 
This is another short line, still within the same paragraph, but with normal space after it. 
This is another short line, but with two line-breaks. 

This is the last line of the paragraph.