Set line spacing

Try the line-height property.

For example, 12px font-size and 4px distant from the bottom and upper lines:

line-height: 20px; /* 4px +12px + 4px */

Or with em units

line-height: 1.7em; /* 1em = 12px in this case. 20/12 == 1.666666  */

You can also use a unit-less value, which is the number of lines: line-height: 2; is double spaced, line-height: 1.5; is one and a half, etc.

You cannot set inter-paragraph spacing in CSS using line-height, the spacing between <p> blocks. That instead sets the intra-paragraph line spacing, the space between lines within a <p> block. That is, line-height is the typographer's inter-line leading within the paragraph is controlled by line-height.

I presently do not know of any method in CSS to produce (for example) a 0.15em inter-<p> spacing, whether using em or rem variants on any font property. I suspect it can be done with more complex floats or offsets. A pity this is necessary in CSS.

If you want condensed lines, you can set same value for font-size and line-height

In your CSS file

.condensedlines {              
    font-size:   10pt;
    line-height: 10pt;  /* try also a bit smaller line-height */
}

In your HTML file

<p class="condensedlines">
bla bla bla bla bla bla <br>
bla bla bla bla bla bla <br>
bla bla bla bla bla bla <br>
</p>

--> Play with this snippet on jsfiddle.net

You can also increase line-height for fine line spacing control:

.mylinespacing {
    font-size:   10pt;
    line-height: 14pt; /* 14 = 10 + 2 above + 2 below */
}