function validate() {
    let submitBtn = document.getElementById('submit');
    let isCompany = false;
    submitBtn.addEventListener('click', (e) => {
        e.preventDefault();
        let username = document.getElementById('username');
        let email = document.getElementById('email');
        let password = document.getElementById('password');
        let confirmPassword = document.getElementById('confirm-password');
        let companyNumber = document.getElementById('companyNumber');
        let validDiv = document.getElementById('valid');
        let allIsValid = true;

        if (username.value.length >= 3 && username.value.length <= 20 && /^[A-Za-z0-9]+$/.test(username.value)) {
            username.style.borderColor = '';
        } else {
            username.style.borderColor = 'red';
            allIsValid = false;
        }

        if (/^[^@.]+@[^@]*\.[^@]*$/.test(email.value)) {
            email.style.borderColor = '';
        } else {
            email.style.borderColor = 'red';
            allIsValid = false;
        }

        if (/^\w{5,15}$/.test(password.value)) {
            password.style.borderColor = '';
        } else {
            password.style.borderColor = 'red';
            allIsValid = false;
        }

        if (/^\w{5,15}$/.test(confirmPassword.value) && confirmPassword.value === password.value) {
            confirmPassword.style.borderColor = '';
        } else {
            confirmPassword.style.borderColor = 'red';
            allIsValid = false;
        }

        if (isCompany) {
            if (Number(companyNumber.value) >= 1000 && Number(companyNumber.value) <= 9999) {
                companyNumber.style.borderColor = '';
            } else {
                companyNumber.style.borderColor = 'red';
                allIsValid = false;
            }
        }

        if (allIsValid) {
            validDiv.style.display = 'block';
        } else {
            validDiv.style.display = 'none';
        }
    });

    let companyInfo = document.getElementById('companyInfo');
    let companyCheckBox = document.getElementById('company');
    companyCheckBox.addEventListener('change', (e) => {
        if (e.target.checked) {
            companyInfo.style.display = 'block';
            isCompany = true;
        } else {
            companyInfo.style.display = 'none';
            isCompany = false;
        }
    });
}