Here is a list of some CSS panels codes.
Panel Animation
Dev: Swarup Kumar Kuila
CSS-only Sliding Panels using transforms
Dev: Shaw
Full-Width Panel Expansion, CSS only
Dev: Shaw
Skewed Flexbox Panels
Dev: Ryan Mulligan
Animated swinging panels/grid
Dev: Seth Abbott
Expanding Sections on hover
Dev: James
Higher Contrast Panels On Patterned Backgrounds
Dev: Paul Hebert
Responsive Flexbox Expanding Panels
Dev: Mark Mead
Pure CSS3 HTML5 sliding panels and off canvas navigation
Dev: Adam Carignan
Panel Switch Interaction with Flexbox and JS
Dev: Susan Lee
Flex Panels Image Gallery
Dev: Joshua Ward
Pure CSS Hover
Dev: XiChen
Multiple Sliding Panels, CSS-only transforms
Dev: Shaw
Dual Sliding Panels
Dev: Ettrics
Pure CSS panels
Dev: Mattia Astorino
Budging Bars | CSS-only Line Bar
Dev: @keyframers
Skewed One Page Scroll
Dev: Nikolay Talanov