// percentages and units are relative to the strokedElement's viewport
UnitProcessor.Context uctx
= UnitProcessor.createContext(ctx, strokedElement);
CSSOMReadOnlyStyleDeclaration decl
= CSSUtilities.getComputedStyle(strokedElement);
CSSValue v;
v = decl.getPropertyCSSValueInternal(CSS_STROKE_WIDTH_PROPERTY);
float width = UnitProcessor.cssOtherLengthToUserSpace
(v, CSS_STROKE_WIDTH_PROPERTY, uctx);