fix: stepper style bleed (#3096)
fix: stepper style bleed (#3096)

stepper specific btn margins were bleeding into other components.
limited it to direct children of stepper__content

closes #3094
Phlow2001/vuetify,vuetifyjs/vuetify,vuetifyjs/vuetify,vuetifyjs/vuetify,Phlow2001/vuetify,Phlow2001/vuetify,Phlow2001/vuetify,Webifi/vuetify,Webifi/vuetify,vuetifyjs/vuetify,Webifi/vuetify