styles.css

.bslib-sidebar-layout>.sidebar>.sidebar-content {
  display: flex;
  flex-direction: column;
  padding: 1.5rem;
}

.bslib-sidebar-layout>.main {
    grid-column: 2 / 3;
    border-top-left-radius: 0;
    border-bottom-left-radius: 0;
    padding: 1.5rem;
}

.shiny-notification {
  position:fixed;
  top: calc(0%);
  left: calc(50% - 150px);
}