Javascript If statement HTML

I have the following code to generate the current date in a specific format. I want to have an if statement that will change the back ground color and the font color depending if the specific day is on a Sunday, Saturday, or a Week day.

var date = new Date();
var dayMonthYear = date.toLocaleString('en-US', {month:'long',day:'numeric',year:'numeric'}).replaceAll(", ", "-");
var weekday = date.toLocaleString('en-US', { weekday: 'long' })
document.write(dayMonthYear + ' [' + weekday + ']');

I thought I would just create a general if statement that looks at the weekday variable but it doesn't seem to work correctly like I would think.

if (weekday = 'Sunday') {
    background-color:aqua;
    color: blue;
    }

Also, any ideas on how to get a - between the Month and Day number?
Example: August-15-2021 My current code generates August 15-2021