styles.css

/* collabora should be in fullscreen if it is opened in a modal dialog */
.collaboramodal.modal.in {
    width: 100%;
    max-width: 100%;
    height: 100%;
    margin: 0;
    padding: 0;
    left: 0;
    top: 0;
}
.collaboramodal.modal.in .modal-body {
    position: absolute;
    width: 100%;
    max-width: 100%;
    height: 100%;
    min-height: 100%;
}
.collaboramodal .modal-dialog {
    width: 100%;
    max-width: 100%;
    height: 100%;
    margin: 0;
    padding-left: 0;
    padding-right: 0;
}
.collaboramodal .modal-header {
    padding-top: 0;
    padding-bottom: 0;
}
.collaboramodal .modal-content {
    width: 100%;
    height: auto;
    min-height: 100%;
    border-radius: 0;
}
.collaboramodal iframe {
    height: 100%;
    width: 100%;
    position: absolute;
    top: 0;
    left: 0;
}

#page-mod-collabora-view.pagelayout-embedded #page {
    padding-left: 0;
}

.collabora-frame.embedded {
    position: fixed;
    height: auto;
    min-height: calc(100% - 25px);
}

/* Some rules for non boost themes like clean */
.collaboramodal.legacy iframe {
    height: 99%;
    width: 99%;
    position: absolute;
    top: 0;
    left: 0;
}
.collaboramodal.legacy.modal.in {
    top: 0;
    z-index: 5000; /* The navbar in clean has z-index: 4030 */
    height: 92%;
    width: 100%;
}
.collaboramodal.legacy.modal.in .modal-body {
    position: absolute;
    width: 99%;
    max-width: 100%;
    height: 100%;
    min-height: 100%;
}