function onLoad() {

var themeSelector = document.getElementById('themeSelector');
for (var themeName in themeMap) {
  var opt = document.createElement('option');
  opt.value = themeName;
  opt.innerHTML = capitalizeFirstLetter(themeName);
  themeSelector.appendChild(opt);
}
if (localStorage.getItem('theme') != null) {
  themeSelector.value = localStorage.getItem('theme');
  toggleTheme();
}

}

function toggleTheme() {

var themeName = themeSelector.value;
localStorage.setItem('theme', themeName);
var element = document.getElementsByTagName('html')[0];
changeTheme(element, themeMap[themeName]);

}

function changeTheme(element, theme) {

element.style.setProperty("--primary-background-color", theme['background-color']);
element.style.setProperty("--primary-text-color", theme['text-color']);
element.style.setProperty("--primary-highlight-color", theme['highlight-color']);

}

function capitalizeFirstLetter(string) {

return string.charAt(0).toUpperCase() + string.slice(1);

}