How to resize workspace for cytoscape?

Question

css

Cytoscape js is called from Here is an example css:
<div id="cy" ></div>

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#cy {
        z-index: 999;
                width: 85%;
                height: 85%;
                float: left;
      }

Or like this:

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#cy {
  width: 50%;
  height: 50%;
  position: relative;
  left: 30;
  top: 0;

}

But for some reason, all my attempts to resize it so that other elements feel it were unsuccessful (