Oh. That's harder. The simplest one of those I can think of offhand is the Project Notes dialog; look in gui.js line 4159. The general blue-top-gray-rest box is a DialogBoxMorph, defined in widgets.js. It's a little complicated because you have to place all the pieces, like that text box and the two buttons in your picture. Where did you get that picture? Maybe you can use it as an example?