CSS Units
CSS has several different units for expressing a length.
Many CSS properties take “length” values, such as width, margin, padding, font-size, etc.
Length is a number followed by a length unit, such as 10px, 2em, etc.
Example
Set different length values, using px (pixels):
h1 {
font-size: 60px;
}
p {
font-size: 25px;
line-height: 50px;
}