yel-dspace-angular/src/app/header/context-help-toggle/context-help-toggle.component.scss

.ds-context-help-toggle {
  color: var(--ds-header-icon-color);
  background-color: var(--ds-header-bg);
}

.ds-context-help-toggle:hover {
  color: var(--ds-header-icon-color-hover);
}