Method one:
Use Quasar's classes. You want some div to have Padding All around? add a .q-pa-md (which stands for quasar-Padding*All-Med*iumsize).
Method two:
Mess with SCSS variables. You can put any of these in your quasar.variables.scss file and hard code various margins to your own liking.
<q-page-container class="q-pa-md">
or
q-page-container.q-pa-md
if you're using pug.