feat: add button to copy code blocks (#228)

BREAKING CHANGE: The `--code-max-height` formatting is applied only to code blocks that use syntax highlighting, see [documentation](https://geekdocs.de/features/code-blocks/).

exampleSite/content/features/code-blocks.md

@@ -2,7 +2,7 @@
 title: Code Blocks
 ---
 
-There are multiple ways to add code blocks. Most of them works out of the box only the Hugo shortcode `<highlight>` need some configuration to work properly.
+There are several ways to add code blocks. Most of them work out of the box, only the Hugo short code `<highlight>` needs to be configured to work properly. The theme also provides some additional features like a copy button and an option to set the maximum length of code blocks. Both of these functions and the dependent formatting rely on the `.highlight` CSS class. You must ensure that you always assign a language to your code blocks if you want to use these functions. If you do not want to apply syntax highlighting, you can also specify `plain` or `text` as the language.
 
 {{< toc >}}
 
@@ -21,14 +21,14 @@ To display an inline shortcode use single quotes:
 Code blocks can be uses without language specification:
 
 ````markdown
-```
+```Plain
 some code
 ```
 ````
 
 **Example:**
 
-```plain
+```Plain
 some code
 ```
 

exampleSite/static/custom.css.example

@@ -23,6 +23,10 @@
   --code-accent-color: #e3e7eb;
   --code-accent-color-lite: #eff1f3;
 
+  --code-copy-font-color: #6b7784;
+  --code-copy-border-color: #adb4bc;
+  --code-copy-success-color: #00c853;
+
   --accent-color: #e9ecef;
   --accent-color-lite: #f8f9fa;
 
@@ -51,6 +55,10 @@
     --code-accent-color: #e3e7eb;
     --code-accent-color-lite: #eff1f3;
 
+    --code-copy-font-color: #6b7784;
+    --code-copy-border-color: #adb4bc;
+    --code-copy-success-color: #00c853;
+
     --accent-color: #e9ecef;
     --accent-color-lite: #f8f9fa;
 
@@ -81,6 +89,10 @@
   --code-accent-color: #262b2f;
   --code-accent-color-lite: #2b3035;
 
+  --code-copy-font-color: #adb4bc;
+  --code-copy-border-color: #808c98;
+  --code-copy-success-color: #00c853;
+
   --accent-color: #2b3035;
   --accent-color-lite: #2f353a;
 
@@ -109,6 +121,10 @@
     --code-accent-color: #262b2f;
     --code-accent-color-lite: #2b3035;
 
+    --code-copy-font-color: #adb4bc;
+    --code-copy-border-color: #808c98;
+    --code-copy-success-color: #00c853;
+
     --accent-color: #2b3035;
     --accent-color-lite: #2f353a;