Improve accessibility: keyboard-operable mobile nav, skip link, focus styles

- Replace the checkbox-hack mobile menu (display:none checkbox was
  unreachable by keyboard/screen readers) with a real button using
  aria-expanded/aria-controls
- Add a skip-to-content link
- Add a consistent :focus-visible outline across interactive elements
- Underline prose links by default instead of only on hover (WCAG 1.4.1
  use-of-color), keep nav/button links unstyled since they're already
  visually distinct
- Respect prefers-reduced-motion for smooth scrolling

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/components/Footer.astro

@@ -51,6 +51,7 @@ const footer = site.footer;
   .footer-nav a {
     color: var(--color-text-muted);
     font-size: var(--font-size-sm);
+    text-decoration: none;
   }
 
   .footer-nav a:hover {

src/components/Nav.astro

@@ -10,14 +10,20 @@ const nav = site.nav;
       <img src={nav.logo} alt={nav.logoAlt} width="320" height="60" class="nav-logo-img" />
     </a>
 
-    <input type="checkbox" id="nav-toggle" class="nav-toggle-checkbox" />
-    <label for="nav-toggle" class="nav-toggle" aria-label="Menü öffnen/schließen">
+    <button
+      type="button"
+      class="nav-toggle"
+      id="nav-toggle"
+      aria-expanded="false"
+      aria-controls="nav-links"
+      aria-label="Menü öffnen"
+    >
       <span></span>
       <span></span>
       <span></span>
-    </label>
+    </button>
 
-    <nav class="nav-links" aria-label="Hauptnavigation">
+    <nav class="nav-links" id="nav-links" aria-label="Hauptnavigation">
       <ul>
         {nav.links.map((item) => (
           <li>
@@ -50,9 +56,6 @@ const nav = site.nav;
     display: flex;
     align-items: center;
     gap: var(--space-3);
-  }
-
-  .nav-logo:hover {
     text-decoration: none;
   }
 
@@ -78,11 +81,11 @@ const nav = site.nav;
     color: var(--color-text-muted);
     font-weight: var(--font-weight-medium);
     font-size: var(--font-size-sm);
+    text-decoration: none;
   }
 
   .nav-links ul a:hover {
     color: var(--color-primary);
-    text-decoration: none;
   }
 
   .nav-cta {
@@ -92,10 +95,6 @@ const nav = site.nav;
     padding: var(--space-3) var(--space-5);
   }
 
-  .nav-toggle-checkbox {
-    display: none;
-  }
-
   .nav-toggle {
     display: none;
     flex-direction: column;
@@ -103,6 +102,9 @@ const nav = site.nav;
     gap: 5px;
     width: 28px;
     height: 22px;
+    padding: 0;
+    background: none;
+    border: none;
     cursor: pointer;
   }
 
@@ -149,8 +151,34 @@ const nav = site.nav;
       border-bottom: 1px solid var(--color-border);
     }
 
-    .nav-toggle-checkbox:checked ~ .nav-links {
+    .nav-links.is-open {
       display: flex;
     }
   }
 </style>
+
+<script>
+  const toggle = document.getElementById('nav-toggle');
+  const links = document.getElementById('nav-links');
+
+  function setOpen(open) {
+    links?.classList.toggle('is-open', open);
+    toggle?.setAttribute('aria-expanded', String(open));
+    toggle?.setAttribute('aria-label', open ? 'Menü schließen' : 'Menü öffnen');
+  }
+
+  toggle?.addEventListener('click', () => {
+    setOpen(!links?.classList.contains('is-open'));
+  });
+
+  links?.addEventListener('click', (event) => {
+    const target = event.target;
+    if (target instanceof HTMLElement && target.tagName === 'A') {
+      setOpen(false);
+    }
+  });
+
+  document.addEventListener('keydown', (event) => {
+    if (event.key === 'Escape') setOpen(false);
+  });
+</script>

src/layouts/Layout.astro

@@ -32,8 +32,9 @@ const fontsHref = googleFontsHref(theme);
     <style set:html={themeCss(theme)} />
   </head>
   <body>
+    <a href="#main-content" class="skip-link">Zum Inhalt springen</a>
     <Nav />
-    <main>
+    <main id="main-content">
       <slot />
     </main>
     <Footer />

src/styles/global.css

@@ -123,11 +123,23 @@ p {
 
 a {
   color: var(--color-primary);
-  text-decoration: none;
+  text-decoration: underline;
+  text-underline-offset: 0.15em;
 }
 
 a:hover {
-  text-decoration: underline;
+  color: var(--color-primary-dark);
+}
+
+a:focus-visible,
+button:focus-visible,
+input:focus-visible,
+textarea:focus-visible,
+summary:focus-visible,
+[tabindex]:focus-visible {
+  outline: 2px solid var(--color-primary);
+  outline-offset: 2px;
+  border-radius: var(--radius-sm);
 }
 
 ul {
@@ -147,6 +159,25 @@ textarea {
   font-size: var(--font-size-base);
 }
 
+.skip-link {
+  position: absolute;
+  top: 0;
+  left: var(--space-4);
+  transform: translateY(-150%);
+  z-index: 100;
+  background: var(--color-primary);
+  color: var(--color-primary-contrast);
+  padding: var(--space-3) var(--space-5);
+  border-radius: 0 0 var(--radius-sm) var(--radius-sm);
+  font-weight: var(--font-weight-semibold);
+  text-decoration: none;
+  transition: transform var(--transition-fast);
+}
+
+.skip-link:focus {
+  transform: translateY(0);
+}
+
 /* ==========================================================================
    Layout-Hilfsklassen
    ========================================================================== */
@@ -249,3 +280,23 @@ textarea {
   border-bottom: 1px dashed var(--color-flag);
   font-style: normal;
 }
+
+/* ==========================================================================
+   Bewegungsreduktion
+   Respektiert die Systemeinstellung fuer Nutzer:innen mit vestibulaeren
+   Beeintraechtigungen (WCAG 2.3.3).
+   ========================================================================== */
+@media (prefers-reduced-motion: reduce) {
+  html {
+    scroll-behavior: auto;
+  }
+
+  *,
+  *::before,
+  *::after {
+    animation-duration: 0.01ms !important;
+    animation-iteration-count: 1 !important;
+    transition-duration: 0.01ms !important;
+    scroll-behavior: auto !important;
+  }
+}