Mobile First Form with sign up using Flexbox

Hi Rom! Clean Solution!

Here is my refactor, I just abstracted the dom manipulation to a function

function checkInputError(errorCondition, inputField, errorText){
    const toggleClass = errorCondition ? inputField.classList.add : inputField.classList.remove;

    toggleClass("active");
    errorText.style.display = errorCondition ? 'block' : "none";
}
    input[0].addEventListener('input', (e) => {
        const value = e.target.value;
        checkInputError(value.length <= 0, input[0], errorTxt[0]); 
    });

    input[1].addEventListener('input', (e) => {
        const value = e.target.value;
        checkInputError(value.length <= 0, input[1], errorTxt[1]); 
    });

    input[2].addEventListener('input', (e) => {
        const value = e.target.value;
        checkInputError(!validateEmail(value), input[2], errorTxt[2]); 
     })

    input[3].addEventListener('input', (e) => {
        const value = e.target.value;
        checkInputError(value.length <= 0, input[3], errorTxt[3]); 
    });

I hope it helps! Cheers!