Our guidelines and reasons for choosing what to override in Reboot:

• We have updated some browser default values to use rems instead of ems or pxs for scalable component spacing.
• In General, We have avoided margin-top. Vertical margins can collapse, yielding unexpected results. More importantly though, a single direction of margin is a simpler mental model.
• For easier scaling across device sizes, we have used rems for spacings and fonts.
• We have kept declarations of font-related properties to a minimum, using inherit whenever possible.
• We have followed bootstrap's themeing and utility naming conventions.