update code sandboxes (#4466)

Author: salazarm

beta/src/pages/blog/2020/02/26/react-v16.13.0.md

@@ -36,7 +36,7 @@ When dynamically applying a `style` that contains longhand and shorthand version
 </div>
 ```
 
-You might expect this `<div>` to always have a red background, no matter the value of `toggle`. However, on alternating the value of `toggle` between `true` and `false`, the background color start as `red`, then alternates between `transparent` and `blue`, [as you can see in this demo](https://codesandbox.io/s/suspicious-sunset-g3jub).
+You might expect this `<div>` to always have a red background, no matter the value of `toggle`. However, on alternating the value of `toggle` between `true` and `false`, the background color start as `red`, then alternates between `transparent` and `blue`, [as you can see in this demo](https://codesandbox.io/s/blue-water-ghx8mi).
 
 **React now detects conflicting style rules and logs a warning.** To fix the issue, don't mix shorthand and longhand versions of the same CSS property in the `style` prop.
 

content/blog/2020-02-26-react-v16.13.0.md

@@ -34,7 +34,7 @@ When dynamically applying a `style` that contains longhand and shorthand version
 </div> 
 ```
 
-You might expect this `<div>` to always have a red background, no matter the value of `toggle`. However, on alternating the value of `toggle` between `true` and `false`, the background color start as `red`, then alternates between `transparent` and `blue`, [as you can see in this demo](https://codesandbox.io/s/suspicious-sunset-g3jub).
+You might expect this `<div>` to always have a red background, no matter the value of `toggle`. However, on alternating the value of `toggle` between `true` and `false`, the background color start as `red`, then alternates between `transparent` and `blue`, [as you can see in this demo](https://codesandbox.io/s/serene-dijkstra-dr0vev).
 
 **React now detects conflicting style rules and logs a warning.** To fix the issue, don't mix shorthand and longhand versions of the same CSS property in the `style` prop.