Darkmode with time

<html>
<head>
<button onclick="darkmode()""dark()">Darkmode</button>
<script>

document.getElementById('darkmode()').onclick = changeColor;
var currentColor = "white";
function changeColor() {
        if(currentColor == "white()"){
           document.body.style.color = "black";
           currentColor = "black";
        } else {-
           document.body.style.color = "white";
           currentColor = "white";
        }
    }

function darkmode() {
        if (document.body.style.backgroundColor == 'rgb(255, 255, 255)') {

                document.body.style.backgroundColor = '#333';
        }
        else {
                document.body.style.backgroundColor = 'rgb(255, 255, 255)';
        }
    }

document.getElementById('dark()').onclick = changeColor;
var currentColor = "white";
function changeColor() {
        if(currentColor == "white"){
           document.body.style.color = "black";
           currentColor = "black";
        } else {
           document.body.style.color = "white";
           currentColor = "white";
        }
    }
    </script>


<script>
function startTime() {
  var today = new Date();
  var h = today.getHours();
  var m = today.getMinutes();
  var s = today.getSeconds();
  m = checkTime(m);
  s = checkTime(s);
  document.getElementById('txt').innerHTML =
  h + ":" + m + ":" + s;
  var t = setTimeout(startTime, 500);
}
function checkTime(i) {
  if (i < 10) {i = "0" + i};
  return i;
}
</script>

</head>

<body onload="startTime()">

<div id="txt"></div>

</body>

<body>
<button id= "dark()">Change color</button>
<script>
document.getElementById('dark()').onclick = changeColor;
var currentColor = "white";
function changeColor() {
        if(currentColor == "white"){
           document.body.style.color = "black";
           currentColor = "black";
        } else {
           document.body.style.color = "white";
           currentColor = "white";
        }
    }
</script>

</body>
</html>