The effects/code that made in the sub form is not taking effect on the parent form. Why?

The effects/code that made in the sub form is not taking effect on the parent form. Why?

The effects/code that made in the sub form is not taking effect on the parent form. I have made a sub form with fields like Part, Part Number etc. Where part is a drop down list and Part Number is a single line. While choosing a part, the corresponding Part number will be displayed in the Part Number Single Line field. While i am inserting the sub form in a parent form, sub form is not working as expected. 

Similarly, i have increased the width of Part drop down list in sub form. But it is not applying while i have inserted it inside other form.

Please give a solution to this problem.