Fix UI font size scaling

studio/frontend/package-lock.json

@@ -85,6 +85,7 @@
         "eslint-plugin-react-hooks": "^7.0.1",
         "eslint-plugin-react-refresh": "^0.5.2",
         "globals": "^17.4.0",
+        "postcss": "^8.5.15",
         "typescript": "~5.9.3",
         "typescript-eslint": "^8.55.0",
         "vite": "^8.0.16"

studio/frontend/package.json

@@ -104,6 +104,7 @@
     "eslint-plugin-react-hooks": "^7.0.1",
     "eslint-plugin-react-refresh": "^0.5.2",
     "globals": "^17.4.0",
+    "postcss": "^8.5.15",
     "typescript": "~5.9.3",
     "typescript-eslint": "^8.55.0",
     "vite": "^8.0.16"

studio/frontend/src/components/shutdown-dialog.tsx

@@ -52,8 +52,8 @@ export function ShutdownDialog({
     onAfterShutdown?.();
     document.body.innerHTML = `
       <div style="display:flex;flex-direction:column;align-items:center;justify-content:center;height:100vh;font-family:sans-serif;gap:12px">
-        <p style="font-size:1.1rem;font-weight:600;margin:0">Unsloth Studio has stopped.</p>
-        <p style="font-size:0.9rem;color:#888;margin:0">You can now close this tab.</p>
+        <p style="font-size:calc(1.1rem * var(--ui-font-scale, 1));font-weight:600;margin:0">Unsloth Studio has stopped.</p>
+        <p style="font-size:calc(0.9rem * var(--ui-font-scale, 1));color:#888;margin:0">You can now close this tab.</p>
       </div>`;
   };
 

studio/frontend/src/features/settings/stores/appearance-custom-store.ts

@@ -510,11 +510,14 @@ export function applyCustomizationToDocument(
     setVar("--custom-chat-font", null);
   }
 
+  // Scale typography without changing the root rem or layout dimensions.
   if (c.uiFontSize !== null && c.uiFontSize !== UI_FONT_SIZE_RANGE.default) {
-    style.fontSize = `${c.uiFontSize}px`;
+    setVar("--ui-font-scale", String(c.uiFontSize / UI_FONT_SIZE_RANGE.default));
   } else {
-    style.removeProperty("font-size");
+    setVar("--ui-font-scale", null);
   }
+  // Clear the root size used by older builds.
+  style.removeProperty("font-size");
 
   if (c.codeFontSize !== null) {
     el.setAttribute("data-code-font-size", "");

studio/frontend/src/features/studio/sections/charts/eval-loss-chart-card.tsx

@@ -17,6 +17,7 @@ import type { ReactElement } from "react";
 import { CartesianGrid, Line, LineChart, XAxis, YAxis } from "recharts";
 import {
   CHART_CONTAINER_CLASS,
+  CHART_FONT_SIZE,
   DEFAULT_CHART_MARGIN,
   DEFAULT_Y_AXIS_WIDTH,
   formatAxisMetric,
@@ -70,7 +71,7 @@ export function EvalLossChartCard({
                 tickLine={false}
                 axisLine={false}
                 tickMargin={8}
-                fontSize={10}
+                fontSize={CHART_FONT_SIZE}
                 tickFormatter={(value) => formatStepTick(Number(value))}
                 interval="preserveStartEnd"
               />
@@ -81,7 +82,7 @@ export function EvalLossChartCard({
                 axisLine={false}
                 tickMargin={8}
                 tickCount={5}
-                fontSize={10}
+                fontSize={CHART_FONT_SIZE}
                 width={DEFAULT_Y_AXIS_WIDTH}
                 tickFormatter={(value) => formatAxisMetric(Number(value))}
               />
@@ -132,7 +133,7 @@ export function EvalLossChartCard({
                   tickLine={false}
                   axisLine={false}
                   tickMargin={8}
-                  fontSize={10}
+                  fontSize={CHART_FONT_SIZE}
                   interval="preserveStartEnd"
                 />
                 <YAxis
@@ -140,7 +141,7 @@ export function EvalLossChartCard({
                   axisLine={false}
                   tickMargin={8}
                   tickCount={5}
-                  fontSize={10}
+                  fontSize={CHART_FONT_SIZE}
                   width={DEFAULT_Y_AXIS_WIDTH}
                 />
                 <Line

studio/frontend/src/features/studio/sections/charts/grad-norm-chart-card.tsx

@@ -15,8 +15,9 @@ import type { ReactElement } from "react";
 import { CartesianGrid, Line, LineChart, XAxis, YAxis } from "recharts";
 import type { ScaleMode } from "./types";
 import {
-  CHART_SYNC_ID,
   CHART_CONTAINER_CLASS,
+  CHART_FONT_SIZE,
+  CHART_SYNC_ID,
   DEFAULT_CHART_MARGIN,
   DEFAULT_Y_AXIS_WIDTH,
   formatAxisMetric,
@@ -78,7 +79,7 @@ export function GradNormChartCard({
               tickLine={false}
               axisLine={false}
               tickMargin={8}
-              fontSize={10}
+              fontSize={CHART_FONT_SIZE}
               tickFormatter={(value) => formatStepTick(Number(value))}
               interval="preserveStartEnd"
             />
@@ -89,7 +90,7 @@ export function GradNormChartCard({
               axisLine={false}
               tickMargin={8}
               tickCount={5}
-              fontSize={10}
+              fontSize={CHART_FONT_SIZE}
               width={DEFAULT_Y_AXIS_WIDTH}
               tickFormatter={(value) => {
                 const num = Number(value);

studio/frontend/src/features/studio/sections/charts/learning-rate-chart-card.tsx

@@ -16,6 +16,7 @@ import { CartesianGrid, Line, LineChart, XAxis, YAxis } from "recharts";
 import type { ScaleMode } from "./types";
 import {
   CHART_CONTAINER_CLASS,
+  CHART_FONT_SIZE,
   CHART_SYNC_ID,
   DEFAULT_CHART_MARGIN,
   DEFAULT_Y_AXIS_WIDTH,
@@ -76,7 +77,7 @@ export function LearningRateChartCard({
               tickLine={false}
               axisLine={false}
               tickMargin={8}
-              fontSize={10}
+              fontSize={CHART_FONT_SIZE}
               tickFormatter={(value) => formatStepTick(Number(value))}
               interval="preserveStartEnd"
             />
@@ -87,7 +88,7 @@ export function LearningRateChartCard({
               axisLine={false}
               tickMargin={8}
               tickCount={5}
-              fontSize={10}
+              fontSize={CHART_FONT_SIZE}
               width={DEFAULT_Y_AXIS_WIDTH}
               tickFormatter={(value) => {
                 const num = Number(value);

studio/frontend/src/features/studio/sections/charts/training-loss-chart-card.tsx

@@ -22,8 +22,9 @@ import {
 } from "recharts";
 import type { ScaleMode } from "./types";
 import {
-  CHART_SYNC_ID,
   CHART_CONTAINER_CLASS,
+  CHART_FONT_SIZE,
+  CHART_SYNC_ID,
   DEFAULT_CHART_MARGIN,
   DEFAULT_Y_AXIS_WIDTH,
   formatAxisMetric,
@@ -96,7 +97,7 @@ export function TrainingLossChartCard({
               tickLine={false}
               axisLine={false}
               tickMargin={8}
-              fontSize={10}
+              fontSize={CHART_FONT_SIZE}
               tickFormatter={(value) => formatStepTick(Number(value))}
               interval="preserveStartEnd"
             />
@@ -107,7 +108,7 @@ export function TrainingLossChartCard({
               axisLine={false}
               tickMargin={8}
               tickCount={5}
-              fontSize={10}
+              fontSize={CHART_FONT_SIZE}
               width={DEFAULT_Y_AXIS_WIDTH}
               tickFormatter={(value) => {
                 const num = Number(value);
@@ -152,7 +153,7 @@ export function TrainingLossChartCard({
                     value: formatMetric(avgRaw),
                   }),
                   position: "insideTopRight",
-                  fontSize: 10,
+                  fontSize: CHART_FONT_SIZE,
                   fill: "#3b82f6",
                 }}
               />

studio/frontend/src/features/studio/sections/charts/utils.ts

@@ -9,6 +9,7 @@ export const DEFAULT_VISIBLE_POINTS = 160;
 export const CHART_CONTAINER_CLASS = "h-[220px] w-full";
 export const DEFAULT_CHART_MARGIN = { top: 4, right: 8, bottom: 0, left: 4 };
 export const DEFAULT_Y_AXIS_WIDTH = 45;
+export const CHART_FONT_SIZE = "calc(10px * var(--ui-font-scale, 1))";
 const TRAILING_ZEROES_RE = /\.?0+$/;
 const NEGATIVE_ZERO_RE = /^-0$/;
 

studio/frontend/src/features/studio/sections/training-section.tsx

@@ -140,13 +140,13 @@ export function TrainingSection() {
                 tickLine={false}
                 axisLine={false}
                 tickMargin={8}
-                fontSize={10}
+                fontSize="calc(10px * var(--ui-font-scale, 1))"
               />
               <YAxis
                 tickLine={false}
                 axisLine={false}
                 tickMargin={8}
-                fontSize={10}
+                fontSize="calc(10px * var(--ui-font-scale, 1))"
               />
               <Line
                 type="monotone"

studio/frontend/src/index.css

@@ -577,6 +577,11 @@ html[data-code-font-size] :is(pre, code, kbd, samp) {
 	font-size: var(--custom-code-font-size) !important;
 }
 
+/* Scale inherited text without changing the root rem used by layout tokens. */
+body {
+	font-size: calc(1rem * var(--ui-font-scale, 1));
+}
+
 /* Pointer cursors: hand cursor over interactive elements. */
 html.pointer-cursors
 	:is(

studio/frontend/vite.config.ts

@@ -4,11 +4,79 @@
 import path from "node:path";
 import tailwindcss from "@tailwindcss/vite";
 import react from "@vitejs/plugin-react";
-import { defineConfig } from "vite";
+import postcss, { type Plugin as PostcssPlugin } from "postcss";
+import { type Plugin as VitePlugin, defineConfig } from "vite";
+
+const UI_FONT_SCALE_VAR = "--ui-font-scale";
+const CSS_WIDE_FONT_SIZE_PATTERN =
+  /^(?:inherit|initial|revert(?:-layer)?|unset|smaller|larger)$/;
+const RELATIVE_FONT_SIZE_PATTERN =
+  /(?:^|[^\w.-])-?(?:\d*\.)?\d+(?:em|ex|cap|ch|ic|lh|rlh|%)\b/;
+const ABSOLUTE_FONT_SIZE_PATTERN =
+  /-?(?:\d*\.)?\d+(?:px|pt|pc|rem|cm|mm|q|in)\b/;
+const FONT_SIZE_FUNCTION_PATTERN = /\b(?:calc|clamp|max|min|var)\(/;
+const CSS_MODULE_ID_PATTERN = /\.css(?:$|\?)/;
+
+// Relative sizes inherit the scale and must not compound through nested text.
+function shouldScaleFontSize(value: string): boolean {
+  const normalized = value.trim().toLowerCase();
+  if (
+    normalized.includes(UI_FONT_SCALE_VAR) ||
+    normalized.includes("--custom-code-font-size") ||
+    CSS_WIDE_FONT_SIZE_PATTERN.test(normalized)
+  ) {
+    return false;
+  }
+
+  // Root rem stays fixed, so rem typography still needs the multiplier.
+  if (RELATIVE_FONT_SIZE_PATTERN.test(normalized)) {
+    return false;
+  }
+
+  return (
+    ABSOLUTE_FONT_SIZE_PATTERN.test(normalized) ||
+    FONT_SIZE_FUNCTION_PATTERN.test(normalized)
+  );
+}
+
+const scaleAbsoluteFontSizes: PostcssPlugin = {
+  postcssPlugin: "unsloth-ui-font-scaling",
+  // biome-ignore lint/style/useNamingConvention: PostCSS visitor API key.
+  Declaration: {
+    "font-size": (declaration) => {
+      if (!shouldScaleFontSize(declaration.value)) {
+        return;
+      }
+      declaration.value = `calc(${declaration.value} * var(${UI_FONT_SCALE_VAR}, 1))`;
+    },
+  },
+};
+
+// Scale named, arbitrary, and vendor font sizes in Tailwind's generated CSS.
+function uiFontScalingPlugin(): VitePlugin {
+  return {
+    name: "unsloth-ui-font-scaling",
+    // Run after Tailwind and before Vite converts CSS into a module.
+    enforce: "pre",
+    async transform(code, id) {
+      if (!CSS_MODULE_ID_PATTERN.test(id)) {
+        return null;
+      }
+      const result = await postcss([scaleAbsoluteFontSizes]).process(code, {
+        from: id,
+        map: false,
+      });
+      if (result.css === code) {
+        return null;
+      }
+      return { code: result.css, map: null };
+    },
+  };
+}
 
 // https://vite.dev/config/
 export default defineConfig({
-  plugins: [react(), tailwindcss()],
+  plugins: [react(), tailwindcss(), uiFontScalingPlugin()],
   optimizeDeps: {
     include: ["@dagrejs/dagre", "@dagrejs/graphlib"],
   },