Docs(DPxAI): Add Subject class-it

subjects/DPxAI/class-it/README.md

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+## Class it!
+
+> Brainpower Mode
+
+### Context
+
+Alright, your being is almost done; some elements still need a bit more shaping, and then we'll make it come to life!
+
+### Resources
+
+We provide you with some content to get started smoothly. Check it out!
+
+- Video [CSS - Set & style with CSS class](https://www.youtube.com/watch?v=-U397k4VloU&list=PLHyAJ_GrRtf979iZZ1N3qYMfsPj9PCCrF&index=6)
+
+### Instructions
+
+If you look at your page, you can observe that some elements come in pairs: the eyes, the arms, and the legs. They are the same organ, one on the left and one on the right; they have exactly the same shape. So for practicality and to avoid repeating the same style twice, we're not going to use their `id` to style them, but a [`class`](https://developer.mozilla.org/en-US/docs/Web/CSS/Class_selectors). Unlike an `id`, a `class` can be attributed to several different elements with common rulesets, so the style defined for that class will apply to all the HTML elements that have it.
+
+#### Task 1
+
+Create the following three classes, set them with the given rulesets, and attribute them to the corresponding HTML elements:
+
+- Class `eye`:
+  - `width` of 60 pixels
+  - `height` of 60 pixels
+  - `background-color` "red"
+  - `border-radius` of 50%
+  - Attributed to `eye-left` & `eye-right`
+- Class `arm`:
+  - `background-color` "aquamarine"
+  - Attributed to `arm-left` & `arm-right`
+- Class `leg`:
+  - `background-color` "dodgerblue"
+  - Attributed to `leg-left` & `leg-right`
+
+Note that you can attribute several classes to the same element. Create the class `body-member`, which sets the `width` to 50 pixels and the `margin` to 30 pixels, and add it to the `class` attribute of these elements: `arm-left`, `arm-right`, `leg-left`, & `leg-right`.
+
+### Code examples
+
+Declare a class `my-first-class` and style it with a `color` to `"blue"` and a `background-color` to `"pink"`:
+
+```css
+.my-first-class {
+  color: blue;
+  background-color: pink;
+}
+```
+
+Apply classes to HTML elements:
+
+```html
+<div class="my-first-class"></div>
+<div class="another-class"></div>
+<div class="my-first-class another-class"></div>
+```
+
+### Expected output
+
+This is what you should see in the browser:
+![](https://github.com/01-edu/public/raw/master/subjects/class-that/class-that.png)
+
+> Need help? Ask your tablemate.
+
+### Notions
+
+- [CSS class](https://developer.mozilla.org/en-US/docs/Web/CSS/Class_selectors)