When "select" is designed to be arranged up and down, the down "select" will block the options of the up "select"
Steps to reproduce:
1.arrange the two "select" up and down
2. add some options to the up "select"
3.the down "select" will block the options of the up "select"
Expected result:
The options of up "select" should have higher z-index than the select
Actual result:
z-index of select--selectize-control--selectize-dropdown is "1"
z-index of select--selectize-control is "2"
