Thank you @a-meshu for your help! Bellow is the working version of my JS function.
async function toggleColor(){
var menuItm = document.getElementsByName('tabLeft').forEach(item =>{
item.addEventListener('click', event=>{
var bg = document.getElementById('tabDiv');
var bgColor = window.getComputedStyle(bg);
bg.setAttribute('style', 'background: linear-gradient(to bottom right, #ec7429, #843f1d)');
console.log("New Color: "+ bgColor);
})
});
}
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