docs: update README.md

Author: 0l1v3rr

README.md

@@ -67,11 +67,24 @@ None of the fields are required. Every query parameter has a default value displ
 | **lineCount** | `?lineCount=2` | 1 | The number of lines you want to add to your card. |
 | **line{n}** | `?line1=html5,html5,auto` | - | The current line of the badge, where {n} is a number. *`(1 <= n <= lineCount)`* |
 
+
+You can customize a theme using these query parameters.  
+These parameters accept only valid hexadecimal colors, otherwise they are not applied. Please use `%23` instead of `#`.
+
+> **Warning**  
+> If the `?theme=` parameter is specified, any of these color customizations will override the theme's values.
+
+| Parameter | Example | Description |
+|-----------|---------|-------------|
+| **bg**    | `?bg=%2383324c` | The color of the background. |
+| **border**    | `?border=%232da7c7` | The color of the border. |
+
 <hr>
 
 ## 🪁 Themes
 These cards come with several built-in themes you can use. You can find all of them by clicking [here](docs/THEMES.md).  
-If you would like to use other themes, and add one for yourself and others, please check this [issue](https://github.com/0l1v3rr/github-readme-tech-stack/issues/2).
+You can customize a theme for yourself using the [query parameters](#-query-parameters).
+If you would like to use other themes, and add one for yourself and others, please check this [issue](https://github.com/0l1v3rr/github-readme-tech-stack/issues/2).  
 
 <hr>
 

docs/THEMES.md

@@ -1,7 +1,7 @@
 ## Supported themes
 
 Here are the currently supported themes spread in a table.  
-If none of these themes fit your needs, feel free to [add one.](https://github.com/0l1v3rr/github-readme-tech-stack/issues/2) Every new theme is welcomed.
+If you would like to use other themes, and add one for yourself and others, please check this [issue](https://github.com/0l1v3rr/github-readme-tech-stack/issues/2).
 
 <table>
   <tr>