HubSpot templates are built using a 12 column responsive-grid system.

Act2 Three Columns Sample

The columns automatically stack one after another on viewport (browser window) sizes smaller than 768px:

Act2 Three Columns Stack Sample

MD Stack

In Act2 you can change the default behavior and make the columns stack at larger viewport size. You can add the md-stack class to a group, and all its direct-child columns will stack on screens smaller than 1140px:

Act2 Template Builder Centered MD-Stack CSS Class

Act2 Three Column MD Stack Sample

Never Stack

Alternatively, if you want the columns to stay that way, even on mobile, you can add this class: never-stack to their direct parent group:

Act2 Never Stack Sample

For advanced users, the Never Stack component has the ability to rewrite the bootstrap grid spans on small or extra small screens, so the content can fit. Apply the classes below to your Never Stack direct child-columns (the combined span number must be 12):

Small Extra Small
ns-sm-span1 ns-xs-span1
ns-sm-span2 ns-xs-span2
ns-sm-span3 ns-xs-span3
ns-sm-span4 ns-xs-span4
ns-sm-span5 ns-xs-span5
ns-sm-span6 ns-xs-span6
ns-sm-span7 ns-xs-span7
ns-sm-span8 ns-xs-span8
ns-sm-span9 ns-xs-span9
ns-sm-span10 ns-xs-span10
ns-sm-span11 ns-xs-span11
ns-sm-span12 ns-xs-span12