File: web/bundles/extjs/resources/theme-bootstrap/theme/stylesheets/bootstrap/default/widgets/_viewport.scss

/**
 * Creates the base structure of Viewport.
 * @member Ext.container.Viewport
 */
@mixin extjs-viewport {
    .#{$prefix}viewport, .#{$prefix}viewport body {
        margin: 0;
        padding: 0;
        border: 0 none;
        overflow: hidden;
        height: 100%;
        position: static;
    }
}