CSS Library: Form CSS: Here
Animated Slide In Search Form
Author: Dynamic Drive
This compact search form starts out as only a small search icon on the page to conserve space. Clicking on the icon slides in and overlays a large search form using the smoothness of CSS3 transitions and transform. On mobile devices, the virtual keyboard is automatically brought up at this point. Clicking anywhere on the page dismisses the search form.
This example integrates the search icon inside a simple relatively positioned header with 3 main elements- a logo on the very left, followed by a UL menu and the search icon on the far right. The icon is from IcoMoon.