Add size part to the guideline

doc/development/ux_guide/illustrations.md

@@ -31,13 +31,38 @@ The illustrations should always align with topics and goals in specific context.
 | -------- | -------- |
 | <img src="img/illustrations-caps-do.png" width= 133px alt="Do: caps and corner" /> | <img src="img/illustrations-caps-don't.png" width= 133px alt="Don't: caps and corner"/> |
-
 #### Radius
 - Standard corner radius: **10px**
 - Depending on the situation, corner radius can be changed to **5px**. For example, when the illustration size is small, an illustration with 10px corner radius would be over-rounded. In this case, the corner radius can be changed to 5px.
 <img src="img/illustrations-border-radius.png" width= 464px alt="Example for border radius"/>
+#### Size
+Depends on the situation, the illustration size can be the 3 types below:
+
+**Large**
+* Use case: Empty states, error pages(e.g. 404, 403)
+* For vertical layout, the illustration should not larger than **430*300 px**.
+* For horizontal layout, the illustration should not larger than **430*380 px**
+
+| Vertocal layout | Horizontal layout |
+| --------------- | ----------------- |
+| <img src="img/illustration-size-large-vertical.png" />  | <img src="img/illustration-size-large-horizontal.png" />
+
+**Medium**
+* Use case: Banner
+* The illustration should not larger than **240*160 px**
+* The illustration should keep simple and clear. We recommend not including too many elements in the medium size illustration.
+
+<img src="img/illustration-size-medium.png" width=983px />
+
+**Small**
+* Use case: Graphics for explanatory text, graphics for status
+* The illustration should not larger than **160*90 px**
+* The illustration should keep simple and clear. We recommend not including too many elements in the small size illustration.
+
+<img src="img/illustration-size-small.png" width=983px />
+
 #### Colors palette
 For consistency, we recommend choosing colors from our color palette.
@@ -47,6 +72,10 @@ For consistency, we recommend choosing colors from our color palette.
 | <img src="img/illustrations-color-orange.png" width= 160px alt="Orange" /> | <img src="img/illustrations-color-purple.png" width= 160px alt="Purple" /> | <img src="img/illustrations-color-grey.png" width= 160px alt="Grey" /> |
 | #FC6D26   | #6B4FBB | #EEEEEE |
+#### Don't
+- Don't include the typography in the illustration.
+- Don't include tanuki in the illustration. If necessary, we recommend having tanuki monochromatic.
+
 ---
 | Orange | Purple |