diff --git a/screenshot.png b/screenshot.png
index af45470..82e5bba 100644
Binary files a/screenshot.png and b/screenshot.png differ
diff --git a/scripts/contrast.mjs b/scripts/contrast.mjs
index ece5621..e7ea6a3 100644
--- a/scripts/contrast.mjs
+++ b/scripts/contrast.mjs
@@ -46,8 +46,86 @@ export function contrastRatio(foreground, background) {
   return (lighter + 0.05) / (darker + 0.05);
 }
 
+function mixHex(foreground, background, foregroundWeight) {
+  const channels = rgbChannels(foreground).map((channel, index) =>
+    Math.round(
+      channel * foregroundWeight +
+        rgbChannels(background)[index] * (1 - foregroundWeight),
+    ),
+  );
+
+  return `#${channels.map((channel) => channel.toString(16).padStart(2, "0")).join("")}`;
+}
+
+const CALLOUT_TYPE_COLORS = {
+  light: {
+    note: "#086ddd",
+    warning: "#ec7500",
+    error: "#e93147",
+    example: "#7852ee",
+    quote: "#9e9e9e",
+    tip: "#00bfbc",
+  },
+  dark: {
+    note: "#027aff",
+    warning: "#e9973f",
+    error: "#fb464c",
+    example: "#a882ff",
+    quote: "#9e9e9e",
+    tip: "#53dfdd",
+  },
+};
+
+const CALLOUT_THEME_CONFIG = {
+  light: {
+    base: "#f8fafc",
+    normal: "#202936",
+    backgroundOpacity: 0.08,
+    titleWeight: 0.52,
+    bodyWeight: 0.5,
+  },
+  dark: {
+    base: "#17191c",
+    normal: "#e7ebf0",
+    backgroundOpacity: 0.12,
+    titleWeight: 0.84,
+    bodyWeight: 0.72,
+  },
+};
+
+export const CALLOUT_CONTRAST_PAIRS = Object.entries(CALLOUT_TYPE_COLORS)
+  .flatMap(([theme, types]) => {
+    const config = CALLOUT_THEME_CONFIG[theme];
+
+    return Object.entries(types).flatMap(([type, semantic]) => {
+      const background = mixHex(
+        semantic,
+        config.base,
+        config.backgroundOpacity,
+      );
+
+      return [
+        [
+          `${theme} callout ${type} title`,
+          mixHex(semantic, config.normal, config.titleWeight),
+          background,
+        ],
+        [
+          `${theme} callout ${type} content`,
+          mixHex(semantic, config.normal, config.bodyWeight),
+          background,
+        ],
+      ];
+    });
+  });
+
+export const ALL_CONTRAST_PAIRS = [
+  ...CORE_CONTRAST_PAIRS,
+  ...CALLOUT_CONTRAST_PAIRS,
+];
+
 export function runContrastCli(
-  pairs = CORE_CONTRAST_PAIRS,
+  pairs = ALL_CONTRAST_PAIRS,
   writeLine = (line) => console.log(line),
 ) {
   let failed = false;
diff --git a/src/components/_callouts.scss b/src/components/_callouts.scss
index a4808fc..ac824ce 100644
--- a/src/components/_callouts.scss
+++ b/src/components/_callouts.scss
@@ -17,7 +17,7 @@ body {
   );
   color: color-mix(
     in srgb,
-    rgb(var(--callout-color)) 72%,
+    rgb(var(--callout-color)) var(--aera-callout-body-semantic-weight),
     var(--text-normal)
   );
   border: 0;
@@ -27,7 +27,7 @@ body {
   padding-inline-end: var(--size-4-12);
   color: color-mix(
     in srgb,
-    rgb(var(--callout-color)) 84%,
+    rgb(var(--callout-color)) var(--aera-callout-title-semantic-weight),
     var(--text-normal)
   );
 }
diff --git a/src/editor/_code.scss b/src/editor/_code.scss
index 294bddf..bc9e03e 100644
--- a/src/editor/_code.scss
+++ b/src/editor/_code.scss
@@ -36,3 +36,11 @@ body {
 :where(.markdown-source-view.mod-cm6 .HyperMD-codeblock) {
   @include monokai-block;
 }
+
+.markdown-source-view.mod-cm6 :where(.HyperMD-codeblock) {
+  white-space: pre;
+  word-break: normal;
+  overflow-wrap: normal;
+  width: max-content;
+  min-width: 100%;
+}
diff --git a/src/foundations/_colors.scss b/src/foundations/_colors.scss
index 11e7277..5a4a6d5 100644
--- a/src/foundations/_colors.scss
+++ b/src/foundations/_colors.scss
@@ -29,6 +29,8 @@
   --aera-inline-code-background: #d9dee5;
   --aera-inline-code-color: #566273;
   --aera-callout-background-opacity: 0.08;
+  --aera-callout-title-semantic-weight: 52%;
+  --aera-callout-body-semantic-weight: 50%;
   --aera-quote-background: #f1f3f6;
   --aera-quote-fold: #d9dee5;
 }
@@ -64,6 +66,8 @@
   --aera-inline-code-background: #2a2f36;
   --aera-inline-code-color: #b8c0cc;
   --aera-callout-background-opacity: 0.12;
+  --aera-callout-title-semantic-weight: 84%;
+  --aera-callout-body-semantic-weight: 72%;
   --aera-quote-background: #22262c;
   --aera-quote-fold: #3a414a;
 }
diff --git a/tests/components.test.mjs b/tests/components.test.mjs
index 14336c1..f8154f7 100644
--- a/tests/components.test.mjs
+++ b/tests/components.test.mjs
@@ -24,6 +24,7 @@ const allowedSelectors = new Set([
   ":where(.markdown-rendered pre:not(.frontmatter))",
   ":where(.markdown-rendered pre:not(.frontmatter)) code[class*=language-]",
   ":where(.markdown-source-view.mod-cm6 .HyperMD-codeblock)",
+  ".markdown-source-view.mod-cm6 :where(.HyperMD-codeblock)",
   ".markdown-rendered blockquote",
   ".markdown-rendered blockquote:not(blockquote blockquote)::before",
   ".markdown-rendered blockquote:not(blockquote blockquote)::after",
@@ -123,7 +124,7 @@ test("uses a borderless semantic callout surface", () => {
     "background-color":
       "rgba(var(--callout-color), var(--aera-callout-background-opacity))",
     color:
-      "color-mix(in srgb, rgb(var(--callout-color)) 72%, var(--text-normal))",
+      "color-mix(in srgb, rgb(var(--callout-color)) var(--aera-callout-body-semantic-weight), var(--text-normal))",
     border: "0",
   });
 });
@@ -136,7 +137,7 @@ test("keeps callout text clear of the watermark", () => {
   assert.deepEqual(Object.fromEntries(title), {
     "padding-inline-end": "var(--size-4-12)",
     color:
-      "color-mix(in srgb, rgb(var(--callout-color)) 84%, var(--text-normal))",
+      "color-mix(in srgb, rgb(var(--callout-color)) var(--aera-callout-title-semantic-weight), var(--text-normal))",
   });
   assert.deepEqual(Object.fromEntries(content), {
     "padding-inline-end": "var(--size-4-12)",
diff --git a/tests/editor-blocks.test.mjs b/tests/editor-blocks.test.mjs
index aa79d29..61becc1 100644
--- a/tests/editor-blocks.test.mjs
+++ b/tests/editor-blocks.test.mjs
@@ -227,3 +227,18 @@ test("styles CM6 code block lines with direct Monokai declarations", () => {
     monokaiDeclarations,
   );
 });
+
+test("keeps CM6 fenced code lines on one horizontal line", () => {
+  assert.deepEqual(
+    directDeclarations(
+      ".markdown-source-view.mod-cm6 :where(.HyperMD-codeblock)",
+    ),
+    [
+      ["white-space", "pre"],
+      ["word-break", "normal"],
+      ["overflow-wrap", "normal"],
+      ["width", "max-content"],
+      ["min-width", "100%"],
+    ],
+  );
+});
diff --git a/tests/foundations.test.mjs b/tests/foundations.test.mjs
index f7cd3e7..2997672 100644
--- a/tests/foundations.test.mjs
+++ b/tests/foundations.test.mjs
@@ -8,6 +8,7 @@ import test from "node:test";
 import { fileURLToPath } from "node:url";
 
 import {
+  CALLOUT_CONTRAST_PAIRS,
   CORE_CONTRAST_PAIRS,
   contrastRatio,
   relativeLuminance,
@@ -73,6 +74,8 @@ const expectedColors = {
     "--aera-inline-code-background": "#d9dee5",
     "--aera-inline-code-color": "#566273",
     "--aera-callout-background-opacity": "0.08",
+    "--aera-callout-title-semantic-weight": "52%",
+    "--aera-callout-body-semantic-weight": "50%",
     "--aera-quote-background": "#f1f3f6",
     "--aera-quote-fold": "#d9dee5",
   },
@@ -105,11 +108,79 @@ const expectedColors = {
     "--aera-inline-code-background": "#2a2f36",
     "--aera-inline-code-color": "#b8c0cc",
     "--aera-callout-background-opacity": "0.12",
+    "--aera-callout-title-semantic-weight": "84%",
+    "--aera-callout-body-semantic-weight": "72%",
     "--aera-quote-background": "#22262c",
     "--aera-quote-fold": "#3a414a",
   },
 };
 
+const calloutTypeColors = {
+  ".theme-light": {
+    note: [8, 109, 221],
+    warning: [236, 117, 0],
+    error: [233, 49, 71],
+    example: [120, 82, 238],
+    quote: [158, 158, 158],
+    tip: [0, 191, 188],
+  },
+  ".theme-dark": {
+    note: [2, 122, 255],
+    warning: [233, 151, 63],
+    error: [251, 70, 76],
+    example: [168, 130, 255],
+    quote: [158, 158, 158],
+    tip: [83, 223, 221],
+  },
+};
+
+function hexChannels(hex) {
+  return [1, 3, 5].map((offset) =>
+    Number.parseInt(hex.slice(offset, offset + 2), 16),
+  );
+}
+
+function mixChannels(foreground, background, foregroundWeight) {
+  return foreground.map(
+    (channel, index) =>
+      channel * foregroundWeight + background[index] * (1 - foregroundWeight),
+  );
+}
+
+function channelLuminance(channel) {
+  const srgb = channel / 255;
+  return srgb <= 0.04045
+    ? srgb / 12.92
+    : ((srgb + 0.055) / 1.055) ** 2.4;
+}
+
+function channelContrastRatio(foreground, background) {
+  const luminance = (channels) => {
+    const [red, green, blue] = channels.map(channelLuminance);
+    return 0.2126 * red + 0.7152 * green + 0.0722 * blue;
+  };
+  const foregroundLuminance = luminance(foreground);
+  const backgroundLuminance = luminance(background);
+
+  return (
+    (Math.max(foregroundLuminance, backgroundLuminance) + 0.05) /
+    (Math.min(foregroundLuminance, backgroundLuminance) + 0.05)
+  );
+}
+
+function calloutSemanticWeight(colorDeclaration, themeDeclarations) {
+  const literal = colorDeclaration.match(
+    /rgb\(var\(--callout-color\)\) ([0-9.]+)%/,
+  );
+  if (literal) return Number(literal[1]) / 100;
+
+  const variable = colorDeclaration.match(
+    /rgb\(var\(--callout-color\)\) var\((--[^)]+)\)/,
+  );
+  assert.ok(variable, colorDeclaration);
+  return Number.parseFloat(themeDeclarations.get(variable[1])) / 100;
+}
+
 for (const [selector, expected] of Object.entries(expectedColors)) {
   test(`${selector} defines the complete Aera color foundation`, () => {
     const declarations = declarationsFor(css, selector);
@@ -120,6 +191,36 @@ for (const [selector, expected] of Object.entries(expectedColors)) {
   });
 }
 
+test("semantic callout titles and content meet WCAG AA in both themes", () => {
+  const roles = [
+    ["title", declarationsFor(css, ".callout-title").get("color")],
+    ["content", declarationsFor(css, ".callout").get("color")],
+  ];
+
+  for (const [themeSelector, types] of Object.entries(calloutTypeColors)) {
+    const theme = declarationsFor(css, themeSelector);
+    const base = hexChannels(theme.get("--color-base-00"));
+    const normal = hexChannels(theme.get("--color-base-100"));
+    const backgroundOpacity = Number.parseFloat(
+      theme.get("--aera-callout-background-opacity"),
+    );
+
+    for (const [type, semantic] of Object.entries(types)) {
+      const background = mixChannels(semantic, base, backgroundOpacity);
+
+      for (const [role, colorDeclaration] of roles) {
+        const weight = calloutSemanticWeight(colorDeclaration, theme);
+        const foreground = mixChannels(semantic, normal, weight);
+        const ratio = channelContrastRatio(foreground, background);
+        assert.ok(
+          ratio >= 4.5,
+          `${themeSelector} ${type} ${role} is ${ratio.toFixed(2)}:1`,
+        );
+      }
+    }
+  }
+});
+
 test("eleven core foreground/background pairs meet WCAG AA contrast", () => {
   assert.deepEqual(CORE_CONTRAST_PAIRS, [
     ["light text", "#202936", "#f8fafc"],
@@ -168,7 +269,12 @@ test("contrast calculation matches WCAG reference endpoints", () => {
   assert.equal(contrastRatio("#647184", "#647184"), 1);
 });
 
-test("contrast CLI prints all eleven pairs", () => {
+test("contrast CLI prints the core and semantic callout pairs", () => {
+  assert.equal(CALLOUT_CONTRAST_PAIRS.length, 24);
+  const allPairs = [
+    ...CORE_CONTRAST_PAIRS,
+    ...CALLOUT_CONTRAST_PAIRS,
+  ];
   const result = spawnSync(
     process.execPath,
     [fileURLToPath(new URL("../scripts/contrast.mjs", import.meta.url))],
@@ -177,8 +283,9 @@ test("contrast CLI prints all eleven pairs", () => {
   const lines = result.stdout.trim().split("\n");
 
   assert.equal(result.status, 0, result.stderr);
-  assert.equal(lines.length, 11);
-  for (const [index, [name]] of CORE_CONTRAST_PAIRS.entries()) {
+  assert.equal(lines.length, 35);
+  for (const [index, [name, foreground, background]] of allPairs.entries()) {
+    assert.ok(contrastRatio(foreground, background) >= 4.5, name);
     assert.match(lines[index], new RegExp(`^PASS ${name}:`));
   }
 });
diff --git a/tests/helpers/css.mjs b/tests/helpers/css.mjs
index 3999cec..c533c38 100644
--- a/tests/helpers/css.mjs
+++ b/tests/helpers/css.mjs
@@ -14,6 +14,7 @@ const allowedThemeSelectors = new Set([
   ":where(.markdown-rendered pre:not(.frontmatter))",
   ":where(.markdown-rendered pre:not(.frontmatter)) code[class*=language-]",
   ":where(.markdown-source-view.mod-cm6 .HyperMD-codeblock)",
+  ".markdown-source-view.mod-cm6 :where(.HyperMD-codeblock)",
   ".markdown-rendered blockquote",
   ".markdown-rendered blockquote:not(blockquote blockquote)::before",
   ".markdown-rendered blockquote:not(blockquote blockquote)::after",
diff --git a/theme.css b/theme.css
index b187a06..cfab98e 100644
--- a/theme.css
+++ b/theme.css
@@ -27,6 +27,8 @@
   --aera-inline-code-background: #d9dee5;
   --aera-inline-code-color: #566273;
   --aera-callout-background-opacity: 0.08;
+  --aera-callout-title-semantic-weight: 52%;
+  --aera-callout-body-semantic-weight: 50%;
   --aera-quote-background: #f1f3f6;
   --aera-quote-fold: #d9dee5;
 }
@@ -59,6 +61,8 @@
   --aera-inline-code-background: #2a2f36;
   --aera-inline-code-color: #b8c0cc;
   --aera-callout-background-opacity: 0.12;
+  --aera-callout-title-semantic-weight: 84%;
+  --aera-callout-body-semantic-weight: 72%;
   --aera-quote-background: #22262c;
   --aera-quote-fold: #3a414a;
 }
@@ -289,6 +293,14 @@ body {
   color: #f8f8f2;
 }
 
+.markdown-source-view.mod-cm6 :where(.HyperMD-codeblock) {
+  white-space: pre;
+  word-break: normal;
+  overflow-wrap: normal;
+  width: max-content;
+  min-width: 100%;
+}
+
 body {
   --callout-border-width: 0px;
   --callout-border-opacity: 0;
@@ -303,13 +315,13 @@ body {
   position: relative;
   overflow: hidden;
   background-color: rgba(var(--callout-color), var(--aera-callout-background-opacity));
-  color: color-mix(in srgb, rgb(var(--callout-color)) 72%, var(--text-normal));
+  color: color-mix(in srgb, rgb(var(--callout-color)) var(--aera-callout-body-semantic-weight), var(--text-normal));
   border: 0;
 }
 
 .callout-title {
   padding-inline-end: var(--size-4-12);
-  color: color-mix(in srgb, rgb(var(--callout-color)) 84%, var(--text-normal));
+  color: color-mix(in srgb, rgb(var(--callout-color)) var(--aera-callout-title-semantic-weight), var(--text-normal));
 }
 
 .callout-content {