Full browser width element with CSS calc()

full-width-calc.css

.container {
    max-width: 1200px;
    width: calc( 100vw - 4rem );
    margin: 0 auto;
}

.container section {
    display: block;
    max-width: 100%;
}

.container section.breakout {
    max-width: 100vw;
    margin: 0 calc( -50vw +50% );
}