The language is modeled after CSS. The selector language has 4 tags (terminal, nonterminal, sequence, stack); wildcard, class, and ID selectors; a :root pseudo-selector; and descendant and child combinators. Specificity and cascading is as in CSS. The possible properties are explained below.

align-items controls vertical alignment of a container's items. It is an inherited property. align-self on an item controls its own alignment, overriding the container. The possible values for both properties are top, center, bottom, and baseline. The default value is top. If two values are given for align-self, they apply to the left and right sides of the item, respectively.

justify-content controls horizontal justification of a container's items. It is an inherited property. The possible values are left, right, start, end, center, space-around, space-between, and space-evenly. The default value is space-between.

Other properties (non-inherited except where noted) are

• flex-absorb, a proportion between 0 and 1, default 0, inherited;
• gap a nonnegative number, default 0;
• continuation-marker, a string, default …; and
• font, up to 4 space-separated strings, being the font family, style, weight, and size, respectively, taking their default values if omitted, which are sans-serif, normal, normal, and 1rem.