main preview gets blank, as I'm not sure how to set alpha in shader graph

I am trying to create dissolve shader. Although i have made the effect but cannot finalise it as it gets blank when i set alpha to alpha in Fragment.(see attached pic)

My aim is to apply the effect shown in Mutiply node next to Fragment node, dissolving with blue border, but the effect in the main preview either gets blank (if connect alpha from split node), or loses border effect ( if connect from multiply node next to alpha in Fragment).

If i give up on adding border effect then it works fine, but i want to add the border effect and that is why I'm struggling with the issue described above.

If anyone knows how to fix this, please help me. Many thanks in advance.