It just doesnt play and the audio is named mario-maker-start.wav
and the start button image is named start-btn.png

        `Style.css:`
        `.start-btn {
         width: 200px;
         height: 50px;
         color: #ffffff;
         background: url('../images/start-btn.png');
         position: absolute;
         bottom: 100px;
         left: 252px;
         border: 2px solid black;}`
        `Index.html:` 

        `<audio id="start" src="sounds/mario-maker-start.wav"></audio>
         <button id=".start-btn">play</button>
         <script>
         var start = document.getElementById(".start-btn");
         function playSound() {
         start.play();}
         startBtn.onclick = playSound;
         </script>
         </body>
         </html>`