// select an element to style
const container = document.querySelector('#container');

// this is not ideal...
container.style.width = '400px;';
container.style.height = '300px';
container.style.top = '0';
container.style.left = '50%';

// let's assign all styles in one go!
Object.assign(container.style, {
  width: '400px',
  height: '300px',
  top: 0,
  left: '50%'
});