I believe what the documentation is saying is that you should avoid including your styles inside of the rendering component:

DO THIS

const StyledWrapper = styled.div`
  /* ... */
`

const Wrapper = ({ message }) => {
  return <StyledWrapper>{message}</StyledWrapper>
}

INSTEAD OF THIS

const Wrapper = ({ message }) => {
  // WARNING: THIS IS VERY VERY BAD AND SLOW, DO NOT DO THIS!!!
  const StyledWrapper = styled.div`
    /* ... */
  `

  return <StyledWrapper>{message}</StyledWrapper>
}

Because what happens is when the component's Props changes, then the component will re-render and the style will regenerate. Therefore it makes sense to keep it separate.

So if you read further on to the Adapting based on props section, they explain this:

const Button = styled.button`
  /* Adapt the colours based on primary prop */
  background: ${props => props.primary ? "palevioletred" : "white"};
  color: ${props => props.primary ? "white" : "palevioletred"};

  font-size: 1em;
  margin: 1em;
  padding: 0.25em 1em;
  border: 2px solid palevioletred;
  border-radius: 3px;
`;

// class X extends React.Component {
//  ...

render(
  <div>
    <Button>Normal</Button>
    <Button primary>Primary</Button>
  </div>
);

// }

this works because when you use the Button component in class X, it will know the props of class X without you having to tell it anything.

For your scenario, I imagine the solution would be simply:

const TabWrapper = styled.li`
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 100px;
  margin: 1px;
  font-size: 3em;
  color: ${props => (props.isSelected ? `white` : `black`)};
  background-color: ${props => (props.isSelected ? `black` : `#C4C4C4`)};
  cursor: ${props => (props.isSelected ? 'default' : `pointer`)};
`;

const Tab = ({ onClick, isSelected, children }) => {
  return <TabWrapper onClick={onClick}>{children}</TabWrapper>
}

const X = <Tab onClick={() => console.log('clicked')} isSelected>Some Children</Tab>

I haven't tested this at all, so please feel free to try it out and let me know if it works for you or whatever worked for you!

There have been some recent developments and with a new version of Typescript (eg. 3.0.1) and styled-components (eg. 3.4.5) there's no need for a separate helper. You can specify the interface/type of your props to styled-components directly.

interface Props {
  onPress: any;
  src: any;
  width: string;
  height: string;
}

const Icon = styled.Image<Props>`
  width: ${p => p.width};
  height: ${p => p.height};
`;

and if you want to be more precise and ignore the onPress

const Icon = styled.Image<Pick<Props, 'src' | 'width' | 'height'>>`
  width: ${p => p.width};
  height: ${p => p.height};
`;