I am trying to implement some code to make a darkmode switch for my website. I am stuck at changing the buttons value to the localstorage saved value. If it loads the value it cant be changed via the button later and if i remove it i need to click the button twice at load to get it to change from the initial wrong value. I get no error messages and don't know how to move forward.

My Javascript

function darkmode() {
  theme = document.getElementById("themebutton");
  if (theme.value == "Dark") {
    theme.value = "Light";
    document.documentElement.setAttribute("data-theme", "light");
    localStorage.setItem("saved", "light");
  } else if (theme.value == "Light") {
    theme.value = "Dark";
    document.documentElement.setAttribute("data-theme", "dark");
    localStorage.setItem("saved", "dark");
  }

function buttonvalue() {
  document.getElementById("themebutton").value = saved;
}

buttonvalue();


window.onload = (event) => {
  if (!localStorage.getItem("saved")) {
    populateStorage();
  } else {
    setStyles();
  }
};

function populateStorage() {
  localStorage.setItem("saved", "light");

  setStyles();
}

function setStyles() {
  document.documentElement.setAttribute("data-theme", saved);
}

My button

<button type="button" id="themebutton" value="Light" onclick="darkmode();">
   dark mode
</button>

Thanks in advance!