Improve mobile hamburger menu color

app/globals.css

@@ -28,6 +28,10 @@
   --card-bg: #ffffff;
   --border-color: #dde4ea;
   --input-border: #c6d2dc;
+  /* Hamburger glyph + 1px border on the menu surface: mvp.css paints every
+     button in --color-bg (the page background), which is invisible here, so
+     the toggle re-drives from this accent (7.8:1 on --surface-color). */
+  --menu-toggle-color: #1f5273;
   /* vizdom WASM graph edges bake black stroke/fill attributes into the SVG;
      palette-driven so the dark theme can swap them to a readable tint. */
   --graph-line: #000000;
@@ -94,6 +98,8 @@ html:root {
   --card-bg: #1a2330;
   --border-color: #2c3a4d;
   --input-border: #5b7396;
+  /* Hamburger glyph + 1px border on the dark menu surface (6.8:1). */
+  --menu-toggle-color: #6fb1d9;
   --graph-line: #9fb0c0;
   --error-color: #f0928c;
   --success-color: #5bbd8b;
@@ -136,6 +142,8 @@ html:root {
     --card-bg: #1a2330;
     --border-color: #2c3a4d;
     --input-border: #5b7396;
+    /* Hamburger glyph + 1px border on the dark menu surface (6.8:1). */
+    --menu-toggle-color: #6fb1d9;
     --graph-line: #9fb0c0;
     --error-color: #f0928c;
     --success-color: #5bbd8b;
@@ -326,7 +334,11 @@ pre {
 .menu-toggle {
   display: none;
   background: none;
-  border: 1px solid var(--input-border);
+  /* mvp.css paints every button in var(--color-bg) — the page background —
+     which is invisible on the menu surface; re-drive glyph and border from
+     the palette so the control stays perceivable in both themes. */
+  color: var(--menu-toggle-color);
+  border: 1px solid var(--menu-toggle-color);
   border-radius: var(--radius);
   font-size: 1.1rem;
   padding: 0.25rem 0.6rem;

tests/unit/theme-css.test.js

@@ -408,6 +408,53 @@ describe('table filter accessibility', () => {
   }
 });
 
+// Hamburger toggle (mobile view): mvp.css paints every button's text in
+// var(--color-bg), and .menu-toggle only overrode background/border, so the
+// ☰ glyph rendered in the page background color and the 1px --input-border
+// edge fell below 3:1 on the menu surface. Both must be re-driven from a
+// per-palette variable.
+describe('menu toggle contrast', () => {
+  /**
+   * Concatenates every declaration block for a selector: the rules map keeps
+   * only the last occurrence (the responsive block) for repeated selectors,
+   * so assertions must run against all of them together.
+   *
+   * @param {string} selector - CSS selector to collect.
+   * @returns {string} Combined declarations.
+   */
+  function combinedRule(selector) {
+    const bodies = [];
+    const ruleRe = /([^{}]+)\{([^{}]*)\}/g;
+    let match;
+    while ((match = ruleRe.exec(noComments)) !== null) {
+      if (match[1].trim() === selector) bodies.push(match[2]);
+    }
+    return bodies.join(';');
+  }
+
+  it('re-drives the glyph and border from the palette', () => {
+    const toggle = combinedRule('.menu-toggle');
+    expect(toggle).toMatch(/(?:^|;)\s*color:\s*var\(--menu-toggle-color\)/);
+    expect(toggle).toMatch(/border:\s*1px solid var\(--menu-toggle-color\)/);
+  });
+
+  for (const [name, palette] of [['light', lightPalette], ['dark', darkPalette]]) {
+    it(`declares a ${name} palette color for the toggle`, () => {
+      expect(palette.get('--menu-toggle-color')).toBeTruthy();
+    });
+
+    it(`the glyph keeps AA text contrast on the menu surface (${name}, SC 1.4.3)`, () => {
+      expect(contrastOf(palette, '--surface-color', '--menu-toggle-color'))
+        .toBeGreaterThanOrEqual(4.5);
+    });
+
+    it(`the border is perceivable on the menu surface (${name}, SC 1.4.11)`, () => {
+      expect(contrastOf(palette, '--surface-color', '--menu-toggle-color'))
+        .toBeGreaterThanOrEqual(3);
+    });
+  }
+});
+
 describe('report CSS selector boundaries', () => {
   it('themes only graph edges and arrowheads, preserving red cycles and node glyphs', () => {
     const fixture = document.createElement('div');