diff --git a/.github/workflows/main.yaml b/.github/workflows/main.yaml
index cc2bf856..b03dc56b 100644
--- a/.github/workflows/main.yaml
+++ b/.github/workflows/main.yaml
@@ -62,7 +62,7 @@ jobs:
       - name: Linter
         if: ${{ github.event_name == 'pull_request' }}
         env:
-          PRE_COMMIT_SKIP: mkdocs-build,linkcheckmd
+          PRE_COMMIT_SKIP: mkdocs-build
         run: |
           pre-commit install
           pre-commit run --all-files --verbose
diff --git a/theme/css/content.css b/theme/css/content.css
index 98023657..75427556 100644
--- a/theme/css/content.css
+++ b/theme/css/content.css
@@ -1020,10 +1020,15 @@ html[data-mode="dim"] .osl-page-hero{
   border-radius: 0;
 }
 
+.osl-side-nav__group a{
+  margin-left: .35rem;
+  padding-left: 1rem;
+}
+
 .osl-side-nav a:hover,
 .osl-side-nav a.active{
   background: transparent;
-  box-shadow: inset 3px 0 0 var(--osl-accent);
+  box-shadow: inset 0 -2px 0 var(--osl-accent);
 }
 
 .project-card,
@@ -1072,3 +1077,164 @@ html[data-mode="dim"] .osl-page-hero{
     padding: 1.25rem 0;
   }
 }
+
+/* Responsive section navigation
+   Desktop keeps the sticky left sidebar; mobile uses an inline disclosure menu
+   so long section menus do not consume half of the viewport. */
+.osl-mobile-section-nav{
+  display: none;
+}
+
+.osl-mobile-section-nav summary{
+  list-style: none;
+}
+
+.osl-mobile-section-nav summary::-webkit-details-marker{
+  display: none;
+}
+
+@media (max-width: 900px){
+  .osl-page-layout{
+    grid-template-columns: 1fr;
+    gap: clamp(1rem, 4vw, 1.6rem);
+  }
+
+  .osl-hero-system,
+  .osl-side-nav{
+    display: none;
+  }
+
+  .osl-mobile-section-nav{
+    display: block;
+    overflow: hidden;
+    border: 1px solid var(--border-strong);
+    border-left: .35rem solid var(--osl-accent);
+    background: var(--surface-solid);
+  }
+
+  .osl-mobile-section-nav__summary{
+    cursor: pointer;
+    display: flex;
+    align-items: center;
+    justify-content: space-between;
+    gap: 1rem;
+    padding: .95rem 1rem;
+    color: var(--heading);
+  }
+
+  .osl-mobile-section-nav__summary:focus-visible,
+  .osl-mobile-section-nav__group-summary:focus-visible{
+    outline: 3px solid color-mix(in oklab, var(--osl-accent) 45%, transparent);
+    outline-offset: -3px;
+  }
+
+  .osl-mobile-section-nav__summary::after{
+    content: "";
+    flex: 0 0 auto;
+    width: .7rem;
+    height: .7rem;
+    border-right: 2px solid currentColor;
+    border-bottom: 2px solid currentColor;
+    transform: translateY(-.15rem) rotate(45deg);
+    transition: transform .18s ease;
+  }
+
+  .osl-mobile-section-nav[open] > .osl-mobile-section-nav__summary::after{
+    transform: translateY(.15rem) rotate(225deg);
+  }
+
+  .osl-mobile-section-nav__summary-text{
+    display: grid;
+    gap: .18rem;
+    min-width: 0;
+  }
+
+  .osl-mobile-section-nav__eyebrow{
+    color: var(--osl-accent);
+    font-size: .76rem;
+    font-weight: 850;
+    letter-spacing: .1em;
+    line-height: 1.2;
+    text-transform: uppercase;
+  }
+
+  .osl-mobile-section-nav__current{
+    overflow: hidden;
+    color: color-mix(in oklab, var(--fg) 78%, var(--muted));
+    font-size: .94rem;
+    font-weight: 750;
+    line-height: 1.3;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+  }
+
+  .osl-mobile-section-nav__panel{
+    display: grid;
+    gap: .15rem;
+    padding: .35rem .75rem .85rem;
+    border-top: 1px solid var(--border);
+  }
+
+  .osl-mobile-section-nav__group{
+    border-top: 1px solid var(--border);
+  }
+
+  .osl-mobile-section-nav__group:first-child{
+    border-top: 0;
+  }
+
+  .osl-mobile-section-nav__group-summary{
+    cursor: pointer;
+    display: flex;
+    align-items: center;
+    justify-content: space-between;
+    gap: .85rem;
+    padding: .82rem .25rem;
+    color: var(--heading);
+    font-size: .95rem;
+    font-weight: 850;
+  }
+
+  .osl-mobile-section-nav__group-summary::after{
+    content: "";
+    flex: 0 0 auto;
+    width: .55rem;
+    height: .55rem;
+    border-right: 2px solid currentColor;
+    border-bottom: 2px solid currentColor;
+    opacity: .7;
+    transform: translateY(-.12rem) rotate(45deg);
+    transition: transform .18s ease;
+  }
+
+  .osl-mobile-section-nav__group[open] > .osl-mobile-section-nav__group-summary{
+    color: var(--osl-accent);
+  }
+
+  .osl-mobile-section-nav__group[open] > .osl-mobile-section-nav__group-summary::after{
+    transform: translateY(.12rem) rotate(225deg);
+  }
+
+  .osl-mobile-section-nav__group-links{
+    display: grid;
+    gap: .12rem;
+    padding: 0 0 .7rem .8rem;
+  }
+
+  .osl-mobile-section-nav a{
+    display: block;
+    padding: .62rem .75rem;
+    color: color-mix(in oklab, var(--fg) 82%, var(--muted));
+    font-size: .93rem;
+    font-weight: 720;
+    line-height: 1.3;
+    text-decoration: none;
+  }
+
+  .osl-mobile-section-nav a:hover,
+  .osl-mobile-section-nav a.active{
+    background: color-mix(in oklab, var(--osl-accent) 10%, transparent);
+    box-shadow: inset 0 -2px 0 var(--osl-accent);
+    color: var(--osl-accent);
+  }
+}
diff --git a/theme/single-sidebar.html b/theme/single-sidebar.html
index 32b673f4..46e793f6 100644
--- a/theme/single-sidebar.html
+++ b/theme/single-sidebar.html
@@ -17,6 +17,80 @@
   {% endif %}
 {% endfor %}
 
+{% macro render_desktop_side_nav(items, current_url) %}
+  <nav>
+    {% set rendered = namespace(urls=[]) %}
+    {% for item in items %}
+      {% if item.children %}
+        <div class="osl-side-nav__group">
+          <span class="osl-side-nav__group-title">{{ item.title }}</span>
+          {% for child in item.children %}
+            {% if child.url not in rendered.urls %}
+            {% set _ = rendered.urls.append(child.url) %}
+            <a href="{{ child.url|url }}"
+               class="{% if child.active or child.url == current_url %}active{% endif %}"
+               {% if child.active or child.url == current_url %}aria-current="page"{% endif %}>
+              {{ child.title }}
+            </a>
+            {% endif %}
+          {% endfor %}
+        </div>
+      {% else %}
+        {% if item.url not in rendered.urls %}
+        {% set _ = rendered.urls.append(item.url) %}
+        <a href="{{ item.url|url }}"
+           class="{% if item.active or item.url == current_url %}active{% endif %}"
+           {% if item.active or item.url == current_url %}aria-current="page"{% endif %}>
+          {{ item.title }}
+        </a>
+        {% endif %}
+      {% endif %}
+    {% endfor %}
+  </nav>
+{% endmacro %}
+
+{% macro render_mobile_side_nav(items, current_url, label) %}
+  <nav class="osl-mobile-section-nav__panel" aria-label="{{ label }} mobile navigation">
+    {% set rendered = namespace(urls=[]) %}
+    {% for item in items %}
+      {% if item.children %}
+        {% set group = namespace(active=item.active) %}
+        {% for child in item.children %}
+          {% if child.active or child.url == current_url %}
+            {% set group.active = true %}
+          {% endif %}
+        {% endfor %}
+        <details class="osl-mobile-section-nav__group" {% if group.active %}open{% endif %}>
+          <summary class="osl-mobile-section-nav__group-summary">
+            {{ item.title }}
+          </summary>
+          <div class="osl-mobile-section-nav__group-links">
+            {% for child in item.children %}
+              {% if child.url not in rendered.urls %}
+              {% set _ = rendered.urls.append(child.url) %}
+              <a href="{{ child.url|url }}"
+                 class="{% if child.active or child.url == current_url %}active{% endif %}"
+                 {% if child.active or child.url == current_url %}aria-current="page"{% endif %}>
+                {{ child.title }}
+              </a>
+              {% endif %}
+            {% endfor %}
+          </div>
+        </details>
+      {% else %}
+        {% if item.url not in rendered.urls %}
+        {% set _ = rendered.urls.append(item.url) %}
+        <a href="{{ item.url|url }}"
+           class="osl-mobile-section-nav__link{% if item.active or item.url == current_url %} active{% endif %}"
+           {% if item.active or item.url == current_url %}aria-current="page"{% endif %}>
+          {{ item.title }}
+        </a>
+        {% endif %}
+      {% endif %}
+    {% endfor %}
+  </nav>
+{% endmacro %}
+
 <section class="osl-page osl-page--sidebar osl-page--section-{{ section_slug }} osl-page--theme-{{ page_theme }}">
   <div class="osl-page-shell">
     <header class="osl-page-hero">
@@ -40,37 +114,19 @@ <h1>{{ page_title or config.site_name }}</h1>
 
     <div class="osl-page-layout">
       {% if sidebar.items %}
+      <details class="osl-mobile-section-nav">
+        <summary class="osl-mobile-section-nav__summary">
+          <span class="osl-mobile-section-nav__summary-text">
+            <span class="osl-mobile-section-nav__eyebrow">{{ sidebar.title }} menu</span>
+            <span class="osl-mobile-section-nav__current">Current: {{ page_title }}</span>
+          </span>
+        </summary>
+        {{ render_mobile_side_nav(sidebar.items, page.url, sidebar.title) }}
+      </details>
+
       <aside class="osl-side-nav" aria-label="{{ sidebar.title }} navigation">
         <p class="osl-side-nav__title">{{ sidebar.title }}</p>
-        <nav>
-          {% set rendered = namespace(urls=[]) %}
-          {% for item in sidebar.items %}
-            {% if item.children %}
-              <div class="osl-side-nav__group">
-                <span class="osl-side-nav__group-title">{{ item.title }}</span>
-                {% for child in item.children %}
-                  {% if child.url not in rendered.urls %}
-                  {% set _ = rendered.urls.append(child.url) %}
-                  <a href="{{ child.url|url }}"
-                     class="{% if child.active or child.url == page.url %}active{% endif %}"
-                     {% if child.active or child.url == page.url %}aria-current="page"{% endif %}>
-                    {{ child.title }}
-                  </a>
-                  {% endif %}
-                {% endfor %}
-              </div>
-            {% else %}
-              {% if item.url not in rendered.urls %}
-              {% set _ = rendered.urls.append(item.url) %}
-              <a href="{{ item.url|url }}"
-                 class="{% if item.active or item.url == page.url %}active{% endif %}"
-                 {% if item.active or item.url == page.url %}aria-current="page"{% endif %}>
-                {{ item.title }}
-              </a>
-              {% endif %}
-            {% endif %}
-          {% endfor %}
-        </nav>
+        {{ render_desktop_side_nav(sidebar.items, page.url) }}
       </aside>
       {% endif %}