improve inline code contrast across all slides

- change code text color from #1e5f8a to #5fb3e4 (brighter blue) in course 223015b
- update code styling in course 223015c for better contrast
- update custom-theme.css with --color-dimmed variable

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

courses/223015c/slides/2026-01-10-termin-2-netzwerke-protokolle-css.md

@@ -12,7 +12,7 @@ title: "Termin 2: Netzwerke, Protokolle & CSS"
 :root {
   --color-foreground: #1a1a2e;
   --color-highlight: #d63384;
-  --color-dimmed: #4a4a6a;
+  --color-dimmed: #dde0e4;
 }
 section.invert {
   --color-foreground: #fff;
@@ -40,8 +40,8 @@ pre code {
   color: inherit;
 }
 code {
-  background: #1a1a2e;
-  color: #d63384;
+  background: #f0e6eb;
+  color: #1a1a2e;
   padding: 0.15em 0.4em;
   border-radius: 4px;
 }