Key Bindings to help write well formed css

Default (OSX).sublime-keymap

[
	{
		"keys": [":"], 
		"command": "insert", 
		"args": {"characters": ": "}, 
		"context": [
			{
				"key": "selector",
				"operator":"equal", 
				"operand":"source.scss"
			},
			{
				"key": "preceding_text", 
				"operator": "regex_match", 
				"operand": "^(?<!.|@|#|&)(\\s*)([a-zA-Z0-9\\-_]*)", 
				"match_all": true 
			}
		]
	},

	{
		"keys": ["{"], 
		"command": "insert_snippet", 
		"args": {"contents": " \\{\n\t$0\n\\}\n"}, 
		"context": [
			{
				"key": "selector",
				"operator":"equal", 
				"operand":"source.scss"
			},
			{
				"key": "preceding_text", 
				"operator": "regex_contains", 
				"operand": "[a-zA-Z0-9)]$", 
				"match_all": true 
			}
		]
	}
]

Add these to your user keybindings file in sublime, currently they only work in an .scss file so if you write plain css or use a different preprocessor, change source.scss to be what you need.

Updated to better match when to add a space after :