Setting height 100% of available space in React

Question

I set height 100% for html, body, and #root in index.js.

<div className="App">
  <Header>
    <SearchForm />
  </Header>
  <div className="wrapper"> <h1 className="font-bold">some text</h1></div>
</div>

Header is 200px height then i set wrapper to 100% height and I see verticall scrollbar. What im doing wrong? Looks like i can scroll value equal to header height.