Reusable styled components (pseudo element) with logic

Question

I've written some shared style to be used across different components, how can I change the value of left or width based a passed value or boolean logic so the values can be more dynamic?

And if possible, I don't want it passed as a prop in the actual component <bar left="20" />, but rather just within the declared styles.

const shared = css`
  ::after {
    content: '';
    left: 0;
    width: 100%;
    ${(props) => props.beta && 
    `
      top: 0;
    `
  }
`

const foo = styled.div`
  ${shared}
`

const bar = styled.div`
  ${shared}

  ${child} {
     ${shared}
  }
`

Answer 1

you can use a funtion instead:

const getShared = (props) => css`
  ::after {
    content: '';
    left: ${props.left || '0'};
    width: ${props.width || '100%'};
    ${(otherProps) => otherProps.beta && 
    `
      top: 0;
    `
  }
`

const foo = styled.div`
  ${(props) => getShared(props)}
`

const bar = styled.div`
  ${(props) => getShared(props)}

  ${child} {
    ${(props) => getShared(props)}
  }
`

if you want to simply override the shared css here is a simple exemple:

<div>
      {/* this is a div that uses shared css */}
      <div css={shared}>this is shared css</div>

      {/* this is a div that uses shared css in his styling*/}
      <FirstContainer>container extends shared css</FirstContainer>

      {/* this is a div that uses shared css in his styling but overrides border color using a prop*/}
      <SecondContainer borderColor="red">container overrriding the shared css</SecondContainer>
 </div>

and here is the styling:

// this is the shared css
export const shared = css`
    width: 100px;
    height: 100px;
    border: solid 1px green;
    margin: 40px;
`

// div using the shared css
export const FirstContainer = styled.div`
    ${shared}
`

// div using the shared css but overriding border color
// props contains all the properties passed to the SecondContainer component (like left in bar component)
export const SecondContainer = styled.div`
    ${shared}

    border-color: ${(props) => props.borderColor}
`

here is the result :