CSS data types - CSS: Cascading Style Sheets
index the data types defined by the set of css specifications include the following: <angle> <angle-percentage> <angular-color-hint> <angular-color-stop> <attr-fallback> <attr-name> <basic-shape> <blend-mode> <calc-product> <calc-sum> <calc-value> <color> <color-stop> <color-stop-angle> <counter-style> <custom-ident> <dimension> <filter-function> <flex> <frequency> <frequency-percentage> <gradient> <ident> <image> <integer> <length> <length-percentage> <number> <number-percentage> <percentage> <position> <quote> <ratio> <resolution> <shape-box> ...

attr() - CSS: Cascading Style Sheets
formal syntax attr( <attr-name> <type-or-unit>?