Stretching div to height of parent

Question

I understand that some variation on this question has been asked many times.

However, I can't seem to get this to work using the recommended methods.

Why is the flex: 1 seemingly being ignored?

The aim is for the red container to fill the available space below it.

CodeSandbox link here.

import React from "react";
import { render } from "react-dom";
import styled, { createGlobalStyle, ThemeProvider } from "styled-components";

const Style = createGlobalStyle`
  body, html {
    height: 100%;
    background: green;
    margin: 0;
    padding: 0;
    overflow-x: hidden;
    overflow-y: auto;
  }
`;

const FlexCol = styled.div`
  display: flex;
  flex-direction: column;
`;

const Layout = ({ children }) => {
  return (
    <div>
      <Header>header</Header>
      <FlexCol>{children}</FlexCol>
    </div>
  );
};

const Header = styled.div`
  height: 50;
  background: blue;
`;

const Home = () => {
  return (
    <div>
      <Feed />
    </div>
  );
};

const FeedContainer = styled.div`
  display: flex;
  flex-direction: column;
  flex: 1;
  background: red;
`;

const Feed = () => <FeedContainer>something</FeedContainer>;

const App = () => {
  return (
    <Layout>
      <Home />
    </Layout>
  );
};

render(
  <ThemeProvider theme={{}}>
    <React.Fragment>
      <Style />
      <App />
    </React.Fragment>
  </ThemeProvider>,
  document.getElementById("root")
);

Answer 1

For future reference, this can also be achieved by styling the Layout and using flexGrow where relevant.

import React from "react";
import { render } from "react-dom";
import styled, { createGlobalStyle, ThemeProvider } from "styled-components";

const Style = createGlobalStyle`
  body, html {
    height: 100%;
    background: green;
    margin: 0;
    padding: 0;
    overflow-x: hidden;
    overflow-y: auto;
  }
`;

const FlexCol = styled.div`
  display: flex;
  flex-direction: column;
  flex-grow: 1;
`;

const Layout = ({ children }) => {
  return (
    <div style={{ height: "100vh", display: "flex", flexDirection: "column" }}>
      <Header>header</Header>
      <FlexCol>{children}</FlexCol>
    </div>
  );
};

const Header = styled.div`
  height: 50;
  background: blue;
`;

const Home = () => {
  return (
    <div
      style={{
        height: "100%"
      }}
    >
      <Feed />
    </div>
  );
};

const FeedContainer = styled.div`
  display: flex;
  flex: 1;
  background: red;
  height: 100%;
  width: 100px;
`;

const Feed = () => <FeedContainer>something</FeedContainer>;

const App = () => {
  return (
    <Layout>
      <Home />
    </Layout>
  );
};

render(
  <ThemeProvider theme={{}}>
    <React.Fragment>
      <Style />
      <App />
    </React.Fragment>
  </ThemeProvider>,
  document.getElementById("root")
);

This gives: