Docs(DPxAI): add subject for colorful-legs

subjects/DPxAI/colorful-legs/README.md

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+## Colorful legs
+
+> JSPowered Mode
+
+### Context
+
+Your robot is cool! but you can make it even more striking! Or at least, make it show off its colorful legs to everyone!
+
+> Follow the instructions, ask your peers if you are stuck and stay motivated because you are close to the goal!
+> Follow every hint you have in the subject!
+> Continue on the code from last exercise, and change the file names!
+
+### Instructions
+
+Just like you turned your robot's arms special in the last exercise, you will do the same now with the legs!
+
+Follow the same
+
+#### Task 1:
+
+Let's put another button in the top right corner of the page with an id `leg-color`, that will change the legs color. Add it in the HTML structure:
+
+```html
+<button id="leg-color">robot's leg colors</button>
+```
+
+Add the button style in the CSS file:
+
+```css
+#leg-color {
+  position: fixed;
+  top: 305px;
+  right: 30px;
+  padding: 10px;
+  margin-bottom: 20px;
+  z-index: 2;
+}
+```
+
+#### Task 2:
+
+In the JS file, like in the previous exercise, get the following elements:
+
+- The button with the ID `leg-color`.
+- The left and right leg elements with the IDs `leg-left` and `leg-right`.
+- Apply the random color to both legs by changing their `backgroundColor`.
+
+**`Prompt Example:`**
+
+- "What mistakes should I prevent while changing the background color of multiple elements in JavaScript?"