pxt-microbit Accessibility PR (#529)

* Accessibility changes

docs/reference/led/fade-in.md

@@ -6,11 +6,11 @@ Gradually increase the [LED screen](/device/screen) brightness until the LED lig
 led.fadeIn(700);
 ```
 
-### Parameters
+## Parameters
 
 * ms - [Number](/types/number); the speed by which the screen brightness is increased, expressed in milliseconds (1,000 milliseconds = 1 second). The smaller the number the faster the screen brightness increased.
 
-### Example: fading dot
+## Example: fading dot
 
 The following code turns on centre LED and then gradually increases and decreases the screen brightness (the centre LED pulses 5 times):
 
@@ -24,7 +24,7 @@ for (let i = 0; i < 5; i++) {
 }
 ```
 
-### See also
+## See also
 
 [brightness](/reference/led/brightness), [fade out](/reference/led/fade-out), [set brightness](/reference/led/set-brightness)