Hi,
The header panel can't be seen inside an paper-dialog (overlay). If I remove the :host {position: relative} from core-header-panel.html, the panel is shown but nothing else can be clicked except the header panel contents.
<paper-dialog opened="true" autoCloseDisabled="true" target="" transition="paper-dialog-transition-bottom">
<core-header-panel mode="waterfall">
<core-toolbar>
<paper-button label="Select" autofocus></paper-button>
<paper-button label="Save"></paper-button>
</core-toolbar>
</core-header-panel>
//other elements
</paper-dialog>
Kr,
Techar