Edit: I managed to get it working by using :has and nesting css classes!

body:has(#theme-toggle:checked) {
  background-color: #eff1f5;
  .content {
    color: #4c4f69;
  }
  .header {
    color: #8839ef
  }
  .nav {
    background-color: #dce0e8;
    color: #4c4f69;
  }
}

I’m making a website for my school’s robotics team and I’m trying to create a dark theme toggle but it’s just not working. I’m trying to avoid javascript and I’ve seen this kind of thing done with only css and html before so I know it’s possible. any advice?

repo: https://github.com/WrenHavoc/JudgeMent-Call-Website

edit: currently my code looks something like this:

#theme-toggle:checked ~ body {
  background-color: #eff1f5;
  color: #fff;
}

#theme-toggle:checked ~ html {
  background-color: #eff1f5;
}

#theme-toggle:checked ~ .content {
  background-color: #eff1f5;
}

the button itself is a checkbox that has display set to none and the label set as an svg so when you click the icon, it gets checked.

<input style="display: none;" type="checkbox" id="theme-toggle">
                <label for="theme-toggle" class="theme-button">
                    <img class="theme-button-svg" src="./icons/half-moon.svg">
                </label>

I used a similar strategy when making the menu for the site so I know it should work

.menu {
  position:absolute;
  margin:0%;
  right:20px;
  top:20px;
}

.menu-button {
  position: relative;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  width: 30px;
  height: 22px;
  cursor: pointer;
  z-index: 2; /* above menu */
}

.menu-button span {
  display: block;
  height: 4px;
  background-color: #cba6f7;
  border-radius: 2px;
  transition: all 0.3s ease;
}

.menu-items {
  top: 30px;
  right: -20px;
  width: 200px;
  background-color: #181825;
  position: absolute;
  display: none;
}

.menu-items li {
  margin: 20px 0;
}

.menu-items a {
  text-decoration: none;
  color: #cba6f7;
  font-size: 18px;
  padding:5px;
}

.menu-items a:hover {
  text-decoration: none;
  background-color: #cba6f7;
  color: #181825;
  font-size: 18px;
}

.menu-selected {
  text-decoration: underline;
  text-decoration-color: #cdd6f4;
  text-decoration-thickness: 3px;
}

.menu-selected:hover {
  text-decoration-color: #181825;
}

#menu:checked ~ .menu-items {
  display: inline;
}

#menu:checked + .menu-button span:nth-child(1) {
  transform: rotate(45deg) translate(5px, 7.5px);
}
#menu:checked + .menu-button span:nth-child(2) {
  opacity: 0;
}
#menu:checked + .menu-button span:nth-child(3) {
  transform: rotate(-45deg) translate(5px, -7.5px);
}

<input style="display: none;" type="checkbox" id="menu">
                <label for="menu" class="menu-button">
                    <span></span>
                    <span></span>
                    <span></span>
                </label>