<!DOCTYPE html>
<html>
<head>
    <title>DOM - CSS</title>
    <script>
        function changeColor(){
            let other_color = 'red'
            let title = document.getElementById('title1')

            if(title.style.color != "blue"){
                document.getElementById('title1').style.color = 'blue'
            } else {
                document.getElementById('title1').style.color = other_color
            }

        }
    </script>
</head>
<body>
    <h1 id="title1" style="color : red">Web title</h1>

    <button type="button" onclick="changeColor()">Change Color</button>
</body>
</html>