If in the Designer and Runtime web.config the Parameter "Forms.Controls.ShowSystemIcons" is set to true, additional Icons will be available for the ToolBar Button.
But currently these are not avaiable as SVG and so they are not available if the Dynamic Theme / Style Sheet is used.
So please convert the PNG Icons to SVG too, as you already do it for the other Icons. That these additional Icons, which are offered in K2 Standard, are available with Dynamic Theme / Style Sheet too.
Thanks