How to insert vertical line without it affecting other elements

Site URL: https://marlin-gopher-jtch.squarespace.com/contact

Hi SS community,

I have two questions regarding a vertical line that I hope you can help with:

1. What is the code to run a vertical line down the full height of a section? 100% does not work. 

2. When I increase the line height, it shifts the text elements down with it. How can I set up this vertical line so that it does not affect the other elements? 

This is the code currently in place:

.vertical-line {
  position: relative;
  background: #000000;
  height: 300px;
  width: 1px;
  margin: 0-auto;
}

Much appreciated 🙂

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