text-decoration-style

Every style is one stroke with a dash pattern, except double and wavy. Double is two strokes of the resolved thickness separated by a gap of the same thickness: the first stroke stays where a single one would sit and the second grows away from the text — downward for an underline and a line-through, upward for an overline. Wavy strokes a curved path instead of a dash pattern (css-text-decor-3 §2.2: "Draw a wavy line") — its centerline grows away from the text the same direction double's second stroke does.

The five styles, as underlines

double on each line, and at a heavier thickness

wavy on each line, at a heavier thickness, and skipping ink

What it is for