Hello Mohammad
The default class, as you correctly stated, will consume 14 Mbps. However, you must keep in mind that these percentages that have been configured (10 for voice, 20 for data) will only take effect if there is congestion. If there is little voice and data traffic, then the default class can consume more than 14Mbps, that is, it consumes any unused bandwidth that may be available from the other classes.
So to answer your question, the default class will use any unused bandwidth from both the voice and data class. Does that make sense?
I hope this has been helpful!
Laz