inner's width is 100%, does it stick out of the outer??

inner has no padding, no margin

content-box

a1

border-box (bootstrap style)

a2

Inners never stick out!

inner has padding but no margin

content-box

b1

border-box (bootstrap style)

b2

Inner in border-box (bootstrap style) won't stick out but it does in content-box!

inner has padding & margin

content-box

c1

border-box (bootstrap style)

c2

Inners always stick out!