You'd better give the selects a specific width. Otherwise, the select will become as wide as the longest option text. Then, after the MultipleSelectPicker has done it's work, the width of the 2 selects will be half of the previous width, resulting in this: option 1 option 2 option 3 option 4 option 5 option 6 option 7 option 8 option 9 option 10

Select with style="width:300px": option 1 option 2 option 3 option 4 option 5 option 6 option 7 option 8 option 9 option 10

Select with colored options: option 1 option 2 option 3 option 4 option 5 option 6 option 7 option 8 option 9 option 10