:root{
/* radii — near-square. Engineering drawings do not have soft corners. */
--radius-0:0;--radius-xs:2px;--radius-s:4px;--radius-m:8px;--radius-pill:999px;
--radius-control:var(--radius-xs);
--radius-panel:var(--radius-0);

/* strokes */
--stroke-hairline:1px; /* @kind other */
--stroke-mid:2px; /* @kind other */
--stroke-heavy:4px; /* @kind other */
--rule-hairline:var(--stroke-hairline) solid var(--border-hairline); /* @kind other */
--rule-strong:var(--stroke-hairline) solid var(--border-strong); /* @kind other */
--rule-accent:var(--stroke-mid) solid var(--border-accent); /* @kind other */

/* elevation — depth comes from contrast and hairlines, not soft shadows */
--shadow-none:none;
--shadow-panel:0 24px 64px rgba(0,0,0,.55);
--shadow-lift:0 8px 24px rgba(0,0,0,.4);
--glow-accent:0 0 0 1px var(--tb-red-40),0 0 32px var(--tb-red-20);
--ring-focus:0 0 0 2px var(--surface-base),0 0 0 4px var(--focus-ring);

/* technical grid overlay (thin engineering lines) */
--grid-overlay:repeating-linear-gradient(90deg,var(--tb-white-06) 0 1px,transparent 1px 120px); /* @kind other */
--blueprint:linear-gradient(var(--tb-white-06) 1px,transparent 1px) 0 0/100% 48px,linear-gradient(90deg,var(--tb-white-06) 1px,transparent 1px) 0 0/48px 100%; /* @kind other */
--blur-panel:blur(18px); /* @kind other */
}