diff --git a/app/config.yml b/app/config.yml
index 86727da..3583105 100644
--- a/app/config.yml
+++ b/app/config.yml
@@ -22,6 +22,7 @@
 # ──────────────────────────────────
 sitename: MD-CMS New Site
 navigation: topbar           # sidebar | topbar
+theme: theme.yml             # presentational config — edit theme.yml to customise colours, fonts, and layout
 
 # homepage: pages/home.md    # override the default landing page
 
@@ -30,20 +31,13 @@ navigation: topbar           # sidebar | topbar
 # favicon: favicon.png
 # footer: "© 2026 Your Name"
 
-# ──────────────────────────────────
-# Typography (optional)
-# ──────────────────────────────────
-# font-title: "Inter:700"
-# font-body: Inter
-# font-code: JetBrains Mono
-
 # ──────────────────────────────────
 # Layout (optional)
 # ──────────────────────────────────
-# main-width: 80em
-# nav-width: 20em
 # nav-position: left         # left | right (sidebar mode)
 
+# Typography and colours are configured in theme.yml, not here.
+
 # ──────────────────────────────────
 # Features (optional)
 # ──────────────────────────────────
diff --git a/app/index.html b/app/index.html
index a80ba18..0f13219 100644
--- a/app/index.html
+++ b/app/index.html
@@ -117,6 +117,11 @@
   --font-body-weight: 400;
   --main-width: 80em;
   --nav-width: 20em;
+  --line-height-body: 1.7;
+  --colour-info: #2563EB;
+  --colour-warning: #D97706;
+  --colour-success: #16A34A;
+  --colour-error: #DC2626;
 }
 
 html { font-size: 16px; scroll-behavior: smooth; }
@@ -126,7 +131,7 @@ body {
   font-weight: var(--font-body-weight);
   color: var(--font-colour);
   background: var(--bg-main);
-  line-height: 1.7;
+  line-height: var(--line-height-body);
   -webkit-font-smoothing: antialiased;
   -moz-osx-font-smoothing: grayscale;
   transition: background-color 0.2s ease, color 0.2s ease;
@@ -1112,6 +1117,53 @@ body {
     applyTheme(current === 'dark' ? 'light' : 'dark');
   }
 
+  function applyThemeYml(tc) {
+    if (!tc) return;
+    const root = document.documentElement;
+    const getOrCreateStyle = id => {
+      let s = document.getElementById(id);
+      if (!s) { s = document.createElement('style'); s.id = id; document.head.appendChild(s); }
+      return s;
+    };
+
+    let modeCss = '';
+    ['light', 'dark'].forEach(mode => {
+      const m = tc[mode];
+      if (!m) return;
+      const vars = [];
+      if (m.accent) {
+        const rgb = hexToRgb(m.accent);
+        vars.push(`--accent: ${m.accent}`);
+        vars.push(`--accent-rgb: ${rgb}`);
+        vars.push(`--nav-active-bg: rgba(${rgb}, 0.10)`);
+        vars.push(`--nav-hover-bg: rgba(${rgb}, 0.05)`);
+        vars.push(`--table-header-bg: rgba(${rgb}, 0.08)`);
+        vars.push(`--link-colour: ${m.accent}`);
+      }
+      if (m.background) { vars.push(`--bg-main: ${m.background}`); vars.push(`--search-bg: ${m.background}`); }
+      if (m['nav-background']) vars.push(`--bg-nav: ${m['nav-background']}`);
+      if (m.text) { vars.push(`--font-colour: ${m.text}`); vars.push(`--code-font: ${m.text}`); }
+      if (m['text-muted']) vars.push(`--font-colour-muted: ${m['text-muted']}`);
+      if (vars.length) modeCss += `:root[data-theme="${mode}"] { ${vars.join('; ')}; }\n`;
+    });
+    if (modeCss) getOrCreateStyle('theme-overrides').textContent = modeCss;
+
+    if (tc['colours-semantic']) {
+      const sem = tc['colours-semantic'];
+      const semVars = [];
+      if (sem.info)    semVars.push(`--colour-info: ${sem.info}`);
+      if (sem.warning) semVars.push(`--colour-warning: ${sem.warning}`);
+      if (sem.success) semVars.push(`--colour-success: ${sem.success}`);
+      if (sem.error)   semVars.push(`--colour-error: ${sem.error}`);
+      if (semVars.length) getOrCreateStyle('theme-semantic').textContent = `:root { ${semVars.join('; ')}; }`;
+    }
+
+    if (tc['main-width']) root.style.setProperty('--main-width', tc['main-width']);
+    if (tc['nav-width'])  root.style.setProperty('--nav-width',  tc['nav-width']);
+    if (tc['line-height']) root.style.setProperty('--line-height-body', String(tc['line-height']));
+    if (tc['font-size'])   document.documentElement.style.fontSize = `${tc['font-size'] * 16}px`;
+  }
+
   function applyConfigTheme() {
     const root = document.documentElement;
     ['light', 'dark'].forEach(mode => {
@@ -1171,35 +1223,48 @@ body {
   }
 
   // ─── Fonts ────────────────────────────────────────────────
-  function loadFonts() {
-    const fonts = {};
-    ['font-title', 'font-body', 'font-code'].forEach(key => {
-      const val = config[key];
-      if (!val) return;
-      const [name, weight] = val.split(':');
-      fonts[key] = { name: name.trim(), weight: weight ? weight.trim() : '400' };
-    });
-    const googleFonts = [];
-    Object.entries(fonts).forEach(([, { name, weight }]) => {
-      googleFonts.push(`${name.replace(/ /g, '+')}:wght@${weight}`);
-    });
+  function loadFonts(tc) {
+    function parseFont(spec) {
+      if (!spec) return null;
+      const parts = spec.split(':');
+      if (parts.length >= 3) return { provider: parts[0].trim(), name: parts.slice(1, -1).join(':').trim(), weight: parts[parts.length - 1].trim() };
+      if (parts.length === 2) return { provider: 'google', name: parts[0].trim(), weight: parts[1].trim() };
+      return { provider: 'google', name: parts[0].trim(), weight: '400' };
+    }
+
+    const src = tc || {};
+    const bodyFont    = parseFont(src['font-body']    || config['font-body']);
+    const headingFont = parseFont(src['font-heading']  || src['font-title'] || config['font-title']);
+    const codeFont    = parseFont(src['font-code']    || config['font-code']);
+    const allFonts    = [bodyFont, headingFont, codeFont].filter(Boolean);
+
+    const bunnyFonts  = allFonts.filter(f => f.provider === 'bunny');
+    const googleFonts = allFonts.filter(f => f.provider === 'google');
+
+    if (bunnyFonts.length) {
+      const link = document.createElement('link');
+      link.rel = 'stylesheet';
+      link.href = `https://fonts.bunny.net/css?family=${bunnyFonts.map(f => `${f.name.replace(/ /g, '+')}:${f.weight}`).join('&family=')}`;
+      document.head.appendChild(link);
+    }
     if (googleFonts.length) {
       const link = document.createElement('link');
       link.rel = 'stylesheet';
-      link.href = `https://fonts.googleapis.com/css2?${googleFonts.map(f => `family=${f}`).join('&')}&display=swap`;
+      link.href = `https://fonts.googleapis.com/css2?${googleFonts.map(f => `family=${f.name.replace(/ /g, '+')}:wght@${f.weight}`).join('&')}&display=swap`;
       document.head.appendChild(link);
     }
+
     const root = document.documentElement;
-    if (fonts['font-title']) {
-      root.style.setProperty('--font-title', `"${fonts['font-title'].name}", system-ui, sans-serif`);
-      root.style.setProperty('--font-title-weight', fonts['font-title'].weight);
+    if (headingFont) {
+      root.style.setProperty('--font-title', `"${headingFont.name}", system-ui, sans-serif`);
+      root.style.setProperty('--font-title-weight', headingFont.weight);
     }
-    if (fonts['font-body']) {
-      root.style.setProperty('--font-body', `"${fonts['font-body'].name}", system-ui, sans-serif`);
-      root.style.setProperty('--font-body-weight', fonts['font-body'].weight);
+    if (bodyFont) {
+      root.style.setProperty('--font-body', `"${bodyFont.name}", system-ui, sans-serif`);
+      root.style.setProperty('--font-body-weight', bodyFont.weight);
     }
-    if (fonts['font-code']) {
-      root.style.setProperty('--font-code', `"${fonts['font-code'].name}", monospace`);
+    if (codeFont) {
+      root.style.setProperty('--font-code', `"${codeFont.name}", monospace`);
     }
   }
 
@@ -2256,14 +2321,23 @@ function fmtDatetime(dtStr) {
         if (link) link.href = `assets/images/${config.logo}`;
       }
 
-      loadFonts();
+      let themeConfig = {};
+      if (config.theme) {
+        try {
+          const themeResp = await fetch(config.theme);
+          if (themeResp.ok) themeConfig = jsyaml.load(await themeResp.text()) || {};
+        } catch (e) { /* fall back to hardcoded CSS defaults */ }
+      }
+
+      loadFonts(themeConfig);
       initCategories();
 
       const navMode = config.navigation || 'sidebar';
       if (navMode === 'topbar') buildTopbar();
       else buildSidebar();
 
-      applyConfigTheme();
+      if (config.theme) applyThemeYml(themeConfig);
+      else applyConfigTheme();
       applyTheme(getInitialTheme());
 
       // nav.yml — phase 2 expects `sections:` + `pages:` blocks; phase 1 flat
diff --git a/app/theme.yml b/app/theme.yml
new file mode 100644
index 0000000..d6fead7
--- /dev/null
+++ b/app/theme.yml
@@ -0,0 +1,66 @@
+# mdcms theme — default
+# Edit colours, fonts, and layout here. See docs for full reference.
+
+# ──────────────────────────────────
+# Colours
+# ──────────────────────────────────
+light:
+  accent: "#2563EB"
+  background: "#FFFFFF"
+  nav-background: "#F8FAFC"
+  text: "#1E293B"
+  text-muted: "#64748B"
+
+dark:
+  accent: "#60A5FA"
+  background: "#0F172A"
+  nav-background: "#1E293B"
+  text: "#F1F5F9"
+  text-muted: "#94A3B8"
+
+# ──────────────────────────────────
+# Semantic colours
+# Used by callout tags (info, warning, success, error).
+# Choose values that work on both light and dark backgrounds.
+# ──────────────────────────────────
+colours-semantic:
+  info: "#2563EB"
+  warning: "#D97706"
+  success: "#16A34A"
+  error: "#DC2626"
+
+# ──────────────────────────────────
+# Callout defaults
+# ──────────────────────────────────
+callouts:
+  info:
+    icon: info
+    primary-colour: "#2563EB"
+    background-colour: "#2563EB"
+  warning:
+    icon: warning
+    primary-colour: "#D97706"
+    background-colour: "#D97706"
+  success:
+    icon: success
+    primary-colour: "#16A34A"
+    background-colour: "#16A34A"
+  error:
+    icon: error
+    primary-colour: "#DC2626"
+    background-colour: "#DC2626"
+
+# ──────────────────────────────────
+# Typography
+# Format: "provider:Font Name:weight"  (provider: bunny | google)
+# ──────────────────────────────────
+font-body: "bunny:Noto Sans:400"
+font-heading: "bunny:Noto Sans:700"
+font-size: 1.0        # unitless multiplier (1.0 = 16px base)
+line-height: 1.7      # unitless multiplier
+
+# ──────────────────────────────────
+# Layout
+# ──────────────────────────────────
+main-width: 80em
+nav-width: 20em