/* MiddleContainer (Start) */
.middleContainer_centering {
}
.middleContainer {
}
@media all and (max-width: 799px) {
.middleContainer {
width: 100%;
}
}
@media all and (min-width: 800px) {
.middleContainer {
width: 800px;
}
}
/* MiddleContainer (End) */

<!-- LR (Init) -->
.lrcontainer {
box-sizing: border-box;
width: 100%;
}
.LR_item {
float: left;
}
.RL_item {
float: right;
}
@media all and (min-width: 800px) {
.lrcontainer_item {
box-sizing: border-box;
width: 50%;
}
}
@media all and (max-width: 799px) {
.lrcontainer_item {
box-sizing: border-box;
width: 100%;
}
}
<!-- LR (Done) -->