#wrapper {
    display: flex;
    flex-direction: column;
    background-color: #ddd;
    width: 900px;
    margin: 0 auto;
}

#box1 {
    width: 100%;
}

.inner_wrapper {
	display: -webkit-flex;
	display: -moz-flex;
	display: -ms-flex;
	display: -o-flex;
	display: flex;
	flex-direction: row;
}

@media (max-width:500px){
	.inner_wrapper {
		flex-direction: column;
		}
	}

#top {
    flex:1;
}

#bottom {
    flex:1;
}