Add this into your keymap file:
[code] { “keys”: “:”], “command”: “insert_snippet”, “args”: {“contents”: “:$0;”}, “context”:
{ "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },
{ "key": "selection_empty", "operator": "equal", "operand": true, "match_all": true },
{ "key": "selector", "operator": "equal", "operand": "source.css - meta.selector.css", "match_all": true },
{ "key": "following_text", "operator": "regex_contains", "operand": "^(?:\t| |\\}|$)", "match_all": true },
{ "key": "preceding_text", "operator": "not_regex_contains", "operand": "&", "match_all": false },
]
},[/code]