/* Stroke widths. 1.5 is absent from the declared scale and is the most-used
   width in the whole document — it draws nearly every boundary in the system. */
:root{
  --stroke-chrome:0.33px;   /* the edge of a translucent bar */
  --stroke-hairline:0.5px;  /* a separator */
  --stroke-thin:1px;        /* a border */
  --stroke-outline:1.5px;   /* the contour of a component — replaces a shadow */
  --stroke-thick:2px;       /* an emphasised border */
  --stroke-heavy:2.5px;     /* the heaviest rule: active cell, current node */
}