The problem in the question was caused by the lack of space around the subtraction operator.
Note that the grammar requires spaces around binary ‘+’ and ‘-’
operators. The ‘*’ and ‘/’ operators do not require spaces.
https://www.w3.org/TR/css3-values/#calc-syntax
This article mentions that the spacing is necessary for unambiguous parsing.
Bad: calc(100%-88px)
Good: calc(100% - 88px)
How do I know it is not recognizing it? Because of the strikethrough
and the yellow triangle icon next to the style rule in chrome dev
tools.
A property that is struck through when viewed in Chrome’s developer tools may be valid but overridden; however, a property struck through and with a warning triangle icon next to it is invalid.
2022 Update – calc()
is supported by all modern browsers in a wide variety of scenarios, though proper spacing is still required.