tweak style of 'search'box in dropdonws

change 'width' of search box in the dropdowns which uses 3rd party plugin for implementation.
Merge branch '73183568add-dropdown' of github.com:gengo/style-guide into 73270894buttons-dropdown
Merge 60cd0d1a69907fae17e6a2704a915ad444594dce into fafb3b6872d22310e5dff13a19c228ecb98d5af4
Travis build 52