The font-stretch CSS descriptor allows authors to specify a normal, condensed, or expanded face for the fonts specified in the @font-face at-rule.
For a particular font family, authors can download various font faces which correspond to the different styles of the same font family, and then use the font-stretch descriptor to explicitly specify the font face's stretch. The values for the CSS descriptor is same as that of its corresponding font property.
A <percentage> value between 50% and 200% (inclusive). Negative values are not allowed for this property.
In earlier versions of the font-stretch specification, the property accepts only the nine keyword values. CSS Fonts Level 4 extends the syntax to accept a <percentage> value as well. This enables variable fonts to offer something more like a continuum of character widths. For TrueType or OpenType variable fonts, the "wdth" variation is used to implement varying widths.
If the font does not provide a face that exactly matches the given value, then values less than 100% map to a narrower face, and values greater than or equal to 100% map to a wider face.
Keyword to numeric mapping
The table below shows the mapping between keyword values and numeric percentages:
Keyword
Percentage
ultra-condensed
50%
extra-condensed
62.5%
condensed
75%
semi-condensed
87.5%
normal
100%
semi-expanded
112.5%
expanded
125%
extra-expanded
150%
ultra-expanded
200%
Variable fonts
Most fonts have a particular width which corresponds to one of the keyterm values. However some fonts, called variable fonts, can support a range of stretching with more or less fine granularity, and this can give the designer a much closer degree of control over the chosen weight. For this, percentage ranges are useful.
For TrueType or OpenType variable fonts, the "wdth" variation is used to implement varying glyph widths.
Accessibility concerns
People with dyslexia and other cognitive conditions may have difficulty reading fonts that are too condensed, especially if the font has a low contrast color ratio.