1. You don't need an if check for the styles of an element you just created. You define the styles of your brand new element.
2. You define a variable named h4 and set it to point to an element, then redefine it later on to equal a string. Weird. Don't do that.
3. You can't access button before it's been defined. It is undefined up until that point.
4. The <h4> tag is empty. Do you want that?
5. Don't use innerHTML to just set text content. Use textContent or innerText instead (innerText keeps the newlines).

Refactored:

const accBtn = document.getElementById('acc-btn');

function acc() {
    const div = document.createElement('div');
    div.classList.add('achi');

    const button = document.createElement('button');
    button.style.display = 'block';
    button.textContent = 'Account'

    const img = document.createElement('img');

    const h4 = document.createElement('h4');
    h4.style.color = 'red';

    div.appendChild(button);
    div.appendChild(img);
    div.appendChild(h4);

    document.getElementById('achi').appendChild(div);
}

accBtn.addEventListener('click', acc);