indicate gmail focus

script.js

function is_non_inbox_node(node){
    var is_non_inbox = false;
    
    if (node.isContentEditable ||
       node.tagName == 'INPUT' ||
       node.tagName == 'TEXTAREA' ||
       node.getAttribute('aria-haspopup') == 'true'
       ){
        is_non_inbox = true;
    }
    
    /* console.log(is_non_inbox, node); */
                
    return is_non_inbox;
}

document.addEventListener('focusin', function(e) {
    if (is_non_inbox_node(e.target)){
        cursor = document.querySelector('.PF.PE');
        cursor.classList.remove('PE');
        cursor.classList.add('PE-hide');
    }
});

document.addEventListener('focusout', function(e) {
    if (is_non_inbox_node(e.target)){
        cursor = document.querySelector('.PF.PE-hide');
        cursor.classList.add('PE');
        cursor.classList.remove('PE-hide');
    }
});

style.css

.f7.nH { 
  /* Add a inbox-style cursor to chat boxes. */
  border-left-width: 5px !important;
}

.PF { 
  /* Make inbox cursor larger. */
  width: 3px !important;
}

I use this with Minmalist for Everything.