diff --git a/site/src/components/ActivityCharts.svelte b/site/src/components/ActivityCharts.svelte
index b80deec..c23eef4 100644
--- a/site/src/components/ActivityCharts.svelte
+++ b/site/src/components/ActivityCharts.svelte
@@ -121,9 +121,27 @@
   // Reset when switching away from a zone-capable metric or leaving histogram
   $: if (!canAlignZones) alignZones = false;
 
+  // ── Theme-aware colours ──────────────────────────────────────────────────
+  function getThemeColors() {
+    const isDark = document.documentElement.getAttribute('data-theme') !== 'light';
+    return {
+      axis:       isDark ? '#71717a' : '#52525b',          // zinc-500 / zinc-600
+      rule:       isDark ? 'rgba(255,255,255,0.25)' : 'rgba(0,0,0,0.2)',
+      tooltipFg:  isDark ? '#ffffff' : '#18181b',
+      tooltipBg:  isDark ? '#09090b' : '#ffffff',          // text outline backing
+      ruleY:      isDark ? '#3f3f46' : '#d4d4d8',          // baseline rule
+    };
+  }
+
   // ── Rendering ────────────────────────────────────────────────────────────
-  onMount(() => { renderChart(); });
-  onDestroy(() => { chart?.remove(); chart = null; });
+  let themeObserver: MutationObserver | null = null;
+
+  onMount(() => {
+    renderChart();
+    themeObserver = new MutationObserver(() => renderChart());
+    themeObserver.observe(document.documentElement, { attributes: true, attributeFilter: ['data-theme'] });
+  });
+  onDestroy(() => { chart?.remove(); chart = null; themeObserver?.disconnect(); });
 
   $: if (chartEl) {
     activeTab; xMode; chartType; histData; histThresholds; alignZones;
@@ -162,6 +180,7 @@
 
   function renderLine(w: number, h: number, yKey: string, yLabel: string, color: string) {
     const x = xMode === 'distance' ? 'dist_km' : 't';
+    const tc = getThemeColors();
     const marks: any[] = [];
 
     if (activeTab === 'cadence') {
@@ -174,12 +193,14 @@
     }
 
     marks.push(
-      Plot.ruleX(data, Plot.pointerX({ x, stroke: 'rgba(255,255,255,0.3)', strokeWidth: 1, strokeDasharray: '4,4' })),
-      Plot.dot(data,  Plot.pointerX({ x, y: yKey, r: 4, fill: color, stroke: 'white', strokeWidth: 1.5 })),
+      Plot.ruleX(data, Plot.pointerX({ x, stroke: tc.rule, strokeWidth: 1, strokeDasharray: '4,4' })),
+      Plot.dot(data,  Plot.pointerX({ x, y: yKey, r: 4, fill: color, stroke: tc.tooltipBg, strokeWidth: 1.5 })),
       Plot.text(data, Plot.pointerX({
         x, y: yKey,
         text: (d: any) => d[yKey] != null ? `${Math.round(d[yKey])}` : '',
-        dy: -12, fill: 'white', fontSize: 11, fontWeight: '600',
+        dy: -12,
+        fill: tc.tooltipFg, stroke: tc.tooltipBg, strokeWidth: 3,
+        fontSize: 11, fontWeight: '600',
       })),
     );
 
@@ -193,7 +214,7 @@
 
     return Plot.plot({
       width: w, height: h, marginLeft: 48, marginBottom: 32,
-      style: { background: 'transparent', color: 'var(--text-4, #a1a1aa)', fontSize: '11px' },
+      style: { background: 'transparent', color: tc.axis, fontSize: '11px' },
       x: { label: null, tickFormat: xTickFormat, grid: false, ticks: 6 },
       y: { label: yLabel, grid: true, tickCount: 4 },
       marks,
@@ -204,6 +225,7 @@
     const yTickFormat = (v: number) => v >= 60 ? `${Math.round(v / 60)}m` : `${v}s`;
     const rawZones = activeTab === 'hr' ? athlete?.hr_zones : activeTab === 'power' ? athlete?.power_zones : null;
     const zoneColors = activeTab === 'hr' ? HR_ZONE_COLORS : PWR_ZONE_COLORS;
+    const tc = getThemeColors();
 
     // ── Zone-aligned: one colored bar per zone ──────────────────────────────
     if (alignZones && rawZones?.length) {
@@ -224,7 +246,7 @@
 
       return Plot.plot({
         width: w, height: h, marginLeft: 48, marginBottom: 32,
-        style: { background: 'transparent', color: 'var(--text-4, #a1a1aa)', fontSize: '11px' },
+        style: { background: 'transparent', color: tc.axis, fontSize: '11px' },
         x: { label: yLabel, grid: false, domain: [clampedZones[0][0], clampedZones[clampedZones.length - 1][1]] },
         y: { label: 'Time', grid: true, tickCount: 4, tickFormat: yTickFormat },
         marks: [
@@ -240,7 +262,7 @@
             fontSize: 10, fontWeight: '600',
             dy: -8,
           }),
-          Plot.ruleY([0], { stroke: '#52525b' }),
+          Plot.ruleY([0], { stroke: tc.ruleY }),
         ],
       });
     }
@@ -251,7 +273,7 @@
         { y: 'count' },
         { x: yKey, fill: color, fillOpacity: 0.7, thresholds: histThresholds },
       )),
-      Plot.ruleY([0], { stroke: '#52525b' }),
+      Plot.ruleY([0], { stroke: tc.ruleY }),
     ];
 
     if (rawZones?.length) {
@@ -282,7 +304,7 @@
 
     return Plot.plot({
       width: w, height: h, marginLeft: 48, marginBottom: 32,
-      style: { background: 'transparent', color: 'var(--text-4, #a1a1aa)', fontSize: '11px' },
+      style: { background: 'transparent', color: tc.axis, fontSize: '11px' },
       x: { label: yLabel, grid: false, ticks: 6, domain: [trimMin, trimMax] },
       y: { label: 'Time', grid: true, tickCount: 4, tickFormat: yTickFormat },
       marks,
diff --git a/site/src/components/MmpChart.svelte b/site/src/components/MmpChart.svelte
index 40e3744..7432f1a 100644
--- a/site/src/components/MmpChart.svelte
+++ b/site/src/components/MmpChart.svelte
@@ -82,6 +82,10 @@
 
   $: colorMap = Object.fromEntries(selectedKeys.map((k, i) => [k, curveColor(k, i)]));
 
+  function getAxisColor() {
+    return document.documentElement.getAttribute('data-theme') === 'light' ? '#52525b' : '#a1a1aa';
+  }
+
   function renderChart(data: typeof plotData, cmap: typeof colorMap) {
     if (!chartEl) return;
     chartEl.innerHTML = '';
@@ -95,7 +99,7 @@
       height: 320,
       marginLeft: 52,
       marginBottom: 40,
-      style: { background: 'transparent', color: '#e4e4e7' },
+      style: { background: 'transparent', color: getAxisColor() },
       x: {
         type: 'log',
         label: 'Duration',
@@ -160,7 +164,9 @@
   onMount(() => {
     const ro = new ResizeObserver(() => renderChart(currentPlotData, currentColorMap));
     ro.observe(chartEl);
-    return () => ro.disconnect();
+    const mo = new MutationObserver(() => renderChart(currentPlotData, currentColorMap));
+    mo.observe(document.documentElement, { attributes: true, attributeFilter: ['data-theme'] });
+    return () => { ro.disconnect(); mo.disconnect(); };
   });
 
   // ── Toggle helpers ─────────────────────────────────────────────────────────