ag-grid Height=100% collapsed

You shall try setting the autoHeight of the ag-grid, by setting the DomLayout.

See the sample code below for angular.

onGridReady(params) {
    this.gridApi = params.api;
    this.gridColumnApi = params.columnApi;

    //The ag-grid is not enlarging based on the page height, 
    //so dynamically adjusting the height of the grid
    this.gridApi.setDomLayout("autoHeight");
}

For reference see this https://plnkr.co/edit/Jb1TD7gbA4w7yclU?preview

.ag-root-wrapper-body.ag-layout-normal.ag-focus-managed {
    height: 100%;
}

This is almost certainly due to you having DOCTYPE html in your html file.

If you do, then you need to ensure that the grids container has a non-0 height to fill, otherwise it will appear as a flat line as you've found.

This is not an ag-Grid specific issue - it's a side effect of not having quirks mode in use.

The easiest thing for you to do is this:

<style>
    html, body {
      width: 100%;
      height: 100%;
    } 

This StackOverflow Question/Answer explains the underlying issue pretty well