add diagonal stripe pattern to klausur and aufgabe class across b course

- update klausur class with 135deg diagonal stripes
- add aufgabe class with solid background
- apply to all termin slides (0-5)

courses/223015b/slides/2025-12-19-termin-0-intro.md

@@ -49,11 +49,23 @@ a {
   color: var(--color-highlight);
 }
 section.klausur {
-  background: #e3f2fd !important;
+  background: repeating-linear-gradient(
+    135deg,
+    #e3f2fd,
+    #e3f2fd 20px,
+    #fff 20px,
+    #fff 40px
+  ) !important;
 }
 section.klausur footer {
   display: none;
 }
+section.aufgabe {
+  background: #e3f2fd !important;
+}
+section.aufgabe footer {
+  display: none;
+}
 </style>
 
 <!-- _class: invert -->

courses/223015b/slides/2026-01-09-termin-2-bild-audio-video.md

@@ -49,11 +49,23 @@ a {
   color: var(--color-highlight);
 }
 section.klausur {
-  background: #e3f2fd !important;
+  background: repeating-linear-gradient(
+    135deg,
+    #e3f2fd,
+    #e3f2fd 20px,
+    #fff 20px,
+    #fff 40px
+  ) !important;
 }
 section.klausur footer {
   display: none;
 }
+section.aufgabe {
+  background: #e3f2fd !important;
+}
+section.aufgabe footer {
+  display: none;
+}
 </style>
 
 <!-- _class: invert -->
@@ -342,7 +354,7 @@ Huffman: Finale Effizienz (wie bei MP3)
 
 ---
 
-# JPEG Quality
+# JPEG Qualität
 
 | Quality | Dateigröße | Artefakte |
 |---------|------------|-----------|
@@ -480,6 +492,8 @@ Lösung: Portfolio-Websites (eigene Kontrolle)
 
 ---
 
+<!-- _class: aufgabe -->
+
 ![bg contain right:25%](./assets/qr/squoosh.png)
 
 # Hands-On: Kompression vergleichen
@@ -893,6 +907,8 @@ MKV vs. MP4: Offenheit vs. Kompatibilität
 
 ---
 
+<!-- _class: aufgabe -->
+
 # Hands-On: Video analysieren
 
 **Aufgabe (40 Min):**

courses/223015b/slides/2026-01-23-termin-3-speichermedien-schnittstellen.md

@@ -49,11 +49,23 @@ a {
   color: var(--color-highlight);
 }
 section.klausur {
-  background: #e3f2fd !important;
+  background: repeating-linear-gradient(
+    135deg,
+    #e3f2fd,
+    #e3f2fd 20px,
+    #fff 20px,
+    #fff 40px
+  ) !important;
 }
 section.klausur footer {
   display: none;
 }
+section.aufgabe {
+  background: #e3f2fd !important;
+}
+section.aufgabe footer {
+  display: none;
+}
 </style>
 
 <!-- _class: invert -->

courses/223015b/slides/2026-01-30-termin-4-distribution-apis-zukunft.md

@@ -49,11 +49,23 @@ a {
   color: var(--color-highlight);
 }
 section.klausur {
-  background: #e3f2fd !important;
+  background: repeating-linear-gradient(
+    135deg,
+    #e3f2fd,
+    #e3f2fd 20px,
+    #fff 20px,
+    #fff 40px
+  ) !important;
 }
 section.klausur footer {
   display: none;
 }
+section.aufgabe {
+  background: #e3f2fd !important;
+}
+section.aufgabe footer {
+  display: none;
+}
 </style>
 
 <!-- _class: invert -->

courses/223015b/slides/2026-xx-xx-termin-5-vertiefung-offene-fragen.md

@@ -49,11 +49,23 @@ a {
   color: var(--color-highlight);
 }
 section.klausur {
-  background: #e3f2fd !important;
+  background: repeating-linear-gradient(
+    135deg,
+    #e3f2fd,
+    #e3f2fd 20px,
+    #fff 20px,
+    #fff 40px
+  ) !important;
 }
 section.klausur footer {
   display: none;
 }
+section.aufgabe {
+  background: #e3f2fd !important;
+}
+section.aufgabe footer {
+  display: none;
+}
 </style>
 
 <!-- _class: invert -->