zoom or window resize issue

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CSS

HTML

Hi there i cant figure how to do a "simple" layout fix:

if i have three div's containing image each one.

<div1> <img src=""> </div>
<div2> <img src=""> </div>
<div3> <img src=""> </div>

i have in lined them to one row so now i can see :

<div1><div2><div3>

if i zoom in the page or re size it this is what i see

<div1>
<div2>
<div3>

my question is how can i prevent the "zoom" & "re-size" changing the site layout.

my goal is that for example: (after "shrink" the page from the right)

<div1><div2><d 

i hope i have explained it right
thanks A LOT.