slack-toggle-sidebar

• Removed css transition for grid layout
• Changed element query selector class

Revamp code for version 4.0.0

• Use ES6 style
• Use extension commands
• Use content script for toggle
• Update manifest version
• Use background scripts
• Enable web accessible resources (css)
• Changed shortcut to Ctrl+Shift+S

Update codes

Add license file
Add css transition #2

Change CSS display from block to flex

Rewrite code for toggle channel sidebar
-- because of slack's changes in their interface

Changed key binding to Cmd + s for mac
and Ctrl + s for windows

Fix message overflow (by @devinrhode2)
Fix CSS to set div#client_body directly

Add Cmd+B to keystroke to show or hide slack sidebar