Philippe You can just add it alongside (no spaces) a value of a proprety so for example the thickness (2px), color blue of a border and font size (0.5 cm) of a paragraph would be :
p { border: 2px blue; font-size: 0.5cm;}
If you want a text shadow (you can use different units when specifying a proprety value, to a certain degree for text shadow ex. inches are too big so they cannot be used),
Text shadow of 2cm x 2pc x 6pt with color blue for paragraph:
p { text-shadow: 2cm 2pc 6pt blue;}
You can use other units like inches (in), milimiters (mm), points (pt) and picas (PC).
If you want to learn more, I suggest going to W3schools website for CSS units:
https://www.w3schools.com/cssref/css_units.asp
Radin Masiha check again your statement is false, you can use cm mm and pc in text shadow, you can even mix them together in a css declaration. Go try this code (below) and you will see!
https://code.sololearn.com/W1m7Riiu0a71/?ref=app
