Niveus: a tactile, adaptive interface language

Bevelled controls with light falling across them, fields as wells, solid
windows, and glass kept for the chrome that floats over everything else.
Warm graphite in dark, soft paper in light, one brand color driving both.
Ships its own fonts (Instrument Sans, JetBrains Mono; OFL).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

niveus/tokens/motion.css

@@ -0,0 +1,107 @@
+/* ==========================================================================
+   Niveus — Motion
+   --------------------------------------------------------------------------
+   Motion explains state and spatial relationship. It is short enough to feel
+   immediate and eased enough to feel physical.
+
+   Rule of thumb: the smaller the element, the faster it moves. A button's
+   hover is 120ms; a dialog's entrance is 240ms.
+   ========================================================================== */
+
+:root {
+  /* --- Duration ------------------------------------------------------------ */
+  --nv-duration-instant: 0ms;
+  --nv-duration-fast: 120ms; /*   hover, press, color change */
+  --nv-duration-quick: 160ms; /*  small elements entering */
+  --nv-duration-normal: 220ms; /* popovers, menus, expansion */
+  --nv-duration-slow: 320ms; /*   dialogs, sheets, large surfaces */
+  --nv-duration-slower: 480ms; /* full-screen transitions */
+
+  /* --- Easing ---------------------------------------------------------------
+     `standard` covers almost everything. Entrance decelerates into place, exit
+     accelerates away, and `spring` is reserved for confirmations — never for
+     anything a user triggers repeatedly. */
+  --nv-ease-standard: cubic-bezier(0.2, 0.05, 0, 1);
+  --nv-ease-entrance: cubic-bezier(0.05, 0.7, 0.1, 1);
+  --nv-ease-exit: cubic-bezier(0.3, 0, 0.8, 0.15);
+  --nv-ease-spring: cubic-bezier(0.34, 1.4, 0.64, 1);
+  --nv-ease-linear: linear;
+
+  /* --- Continuity -------------------------------------------------------------
+     Durations for changes the user is meant to *follow*, not merely notice.
+     They are longer than an interaction response because the eye has further
+     to travel: emphasis crossing a navigation bar, a panel growing open, a
+     whole surface changing appearance. */
+  --nv-duration-travel: 260ms; /* emphasis moving from one element to another */
+  --nv-duration-expand: 280ms; /* content growing out of, or back into, place */
+  --nv-duration-theme: 400ms; /*  the entire surface changing appearance */
+
+  /* Leaves quickly, lands softly. The right curve for something travelling a
+     distance the user is meant to follow with their eye. */
+  --nv-ease-emphasized: cubic-bezier(0.32, 0.04, 0.06, 1);
+
+  /* --- Composites ------------------------------------------------------------
+     `translate` and `scale` are listed rather than `transform`, because the
+     components animate the individual properties — a transition on `transform`
+     does not cover them, and the movement snaps. */
+  --nv-transition-colors:
+    color var(--nv-duration-fast) var(--nv-ease-standard),
+    background-color var(--nv-duration-fast) var(--nv-ease-standard),
+    border-color var(--nv-duration-fast) var(--nv-ease-standard);
+  --nv-transition-depth:
+    box-shadow var(--nv-duration-fast) var(--nv-ease-standard),
+    translate var(--nv-duration-fast) var(--nv-ease-standard),
+    scale var(--nv-duration-fast) var(--nv-ease-standard);
+  --nv-transition-control:
+    color var(--nv-duration-fast) var(--nv-ease-standard),
+    background-color var(--nv-duration-fast) var(--nv-ease-standard),
+    border-color var(--nv-duration-fast) var(--nv-ease-standard),
+    box-shadow var(--nv-duration-fast) var(--nv-ease-standard),
+    translate var(--nv-duration-fast) var(--nv-ease-standard),
+    scale var(--nv-duration-fast) var(--nv-ease-standard);
+
+  /* Containers: the same as depth, plus the colors, so a surface glides into
+     its new appearance when the theme changes instead of snapping. */
+  --nv-transition-surface:
+    color var(--nv-duration-fast) var(--nv-ease-standard),
+    background-color var(--nv-duration-fast) var(--nv-ease-standard),
+    border-color var(--nv-duration-fast) var(--nv-ease-standard),
+    box-shadow var(--nv-duration-fast) var(--nv-ease-standard),
+    translate var(--nv-duration-fast) var(--nv-ease-standard),
+    scale var(--nv-duration-fast) var(--nv-ease-standard);
+
+  --nv-transition-expand:
+    block-size var(--nv-duration-expand) var(--nv-ease-standard),
+    grid-template-rows var(--nv-duration-expand) var(--nv-ease-standard),
+    opacity var(--nv-duration-expand) var(--nv-ease-standard);
+
+  /* --- Displacement ----------------------------------------------------------
+     How far things move. Presses sink by 1px; surfaces enter from 8px away. */
+  --nv-lift-hover: -1px;
+  --nv-press-depth: 1px;
+  --nv-travel-sm: 4px;
+  --nv-travel-md: 8px;
+  --nv-travel-lg: 16px;
+}
+
+/* Reduced motion is a system-wide contract, not a per-component opt-in: cut
+   duration to near-zero and neutralise displacement, but keep transitions
+   alive so state changes still resolve rather than snapping mid-flight. */
+@media (prefers-reduced-motion: reduce) {
+  :root {
+    --nv-duration-fast: 1ms;
+    --nv-duration-quick: 1ms;
+    --nv-duration-normal: 1ms;
+    --nv-duration-slow: 1ms;
+    --nv-duration-slower: 1ms;
+    --nv-duration-travel: 1ms;
+    --nv-duration-expand: 1ms;
+    --nv-duration-theme: 1ms;
+    --nv-ease-spring: var(--nv-ease-standard);
+    --nv-lift-hover: 0px;
+    --nv-press-depth: 0px;
+    --nv-travel-sm: 0px;
+    --nv-travel-md: 0px;
+    --nv-travel-lg: 0px;
+  }
+}