how to set image size in flexbox code example

Example: css flexbox image

/********** What to do in case of <div> containing images?  ***********

In this case, the "flex" property is no longer effective in regulating 
the size of the items (<div>) inside the container. This happens because 
the size of the image itself will impact the <div>. So, to force the 
image to fit the desired size, we need to do the following: */

.big_container {
  display: flex;
  flex-wrap: wrap;    
}

div {
  flex: 1;       
}

img {
  width: 100%;        /* Make it occupy 100% of the size of the <div> */
  min-width: 280px;   /* Give it a minimum size so that it will wrap 
                         instead of just shrinking */
}