The <ratio>CSS data type, used for describing aspect ratios in media queries, denotes the proportion between two unitless values. It is a strictly positive <integer> followed by a slash ('/', Unicode U+002F SOLIDUS) and a second strictly positive <integer>. There may be spaces before and after the solidus.
Traditional TV format in the 20th century.
Modern, 'widescreen', TV format.
185/100 = 91/50 (non-integer dividends and divisors are not allowed)
The most common movie format since the 1960s.
239/100 (non-integer dividends and divisors are not allowed)