Created a little darkmode toggle button with pure CSS.

Code:

<style>
  #darkmode-switch {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
  }

  #darkmode-switch input {
    display: none;
  }

  #darkmode-switch label {
    position: relative;
    display: block;
    width: 70px;
    height: 35px;
    border-radius: 45px;
    background: rgb(76, 170, 233);
    transition: background-color 0.5s;
  }

  #darkmode-switch label .cloud {
    position: absolute;
    display: block;
    border-radius: 5px;
    background: rgb(176, 215, 241);
    transition: all 0.4s cubic-bezier(0.7, -0.5, 0.25, 1.5);
  }

  #darkmode-switch label .cloud:nth-child(1) {
    top: 11px;
    right: 12px;
    height: 6px;
    width: 14px;
  }

  #darkmode-switch label .cloud:nth-child(2) {
    top: 18px;
    right: 18px;
    width: 6px;
    height: 3px;
  }

  #darkmode-switch input:checked ~ label {
    background-color: rgb(23, 76, 109);
  }

  #darkmode-switch input:checked ~ label .cloud {
    transform: translateX(-27px);
    width: 3px;
    height: 3px;
    background: rgb(104, 144, 168);
  }

  #darkmode-switch label::after {
    box-sizing: border-box;
    content: '';
    display: block;
    position: absolute;
    width: 25px;
    height: 25px;
    margin: 5px;
    left: 0;
    top: 0;
    border-radius: 20px;
    background: rgb(235, 201, 108);
    transition: all 0.4s cubic-bezier(0.7, -0.5, 0.25, 1.5);
  }

  #darkmode-switch input:checked ~ label::after {
    left: 35px;
    box-shadow: 10px 6px 0 0 rgb(235, 201, 108);
    transform: translate(-10px, -6px);
    background: transparent;
  }
</style>

<div id="darkmode-switch">
  <input type="checkbox" id="darkmode-switch-radio" />
  <label for="darkmode-switch-radio">
    <span class="cloud"></span>
    <span class="cloud"></span>
  </label>
</div>