<div class="container">
  <label for="switch">
    <input type="checkbox" id="switch">
    <div class="toggle-wrapper">
    <div class="day-night">
    </div>
    <div class="tree-left">
      <div class="tree"></div>
      <div class="trunk">
        <div class="branch"></div>
        <div class="branch"></div>
      </div>
    </div>
    <div class="tree-right">
      <div class="tree-back">
        <div class="trunk"></div>
      </div>
      <div class="tree-front">
        <div class="trunk"></div>
      </div>
    </div>
    <div class="moon"></div>
    <div class="stars">
      <div class="star big-star">
        <div class="vertical"></div>
        <div class="horizontal"></div>
      </div>
      <div class="star small-star">
        <div class="vertical"></div>
        <div class="horizontal"></div>
      </div>
    </div>
    <div class="sun"></div>
    <div class="hills">
      <div class="hill-left"></div>
      <div class="hill-right"></div>
    </div>
  </div>
  </label>
</div>
  
* {
  box-sizing: border-box;
}
html, body {
  width: 100%;
  height: 100%;
  margin: 0;
}
html{
  --wrapper-bg: #9bb7e8;
  --hill-left: #5c6090;
  --hill-right: #4b4f85;
  --sky-bg-night: linear-gradient(to bottom, rgba(185,147,212,1) 0%, rgba(230,224,237,1) 65%);
  --tree-trunk: #3b3853;
  --tree: rgba(76,80,139,1);
  --sun: linear-gradient(24deg, rgba(255,219,156,1) 0%, rgba(254,195,87,1) 53%);
  --day-night: rgba(242, 198, 160, 0.6);
}
html.switch {
  --wrapper-bg: #111827;
  --hill-left: #602291;
  --hill-right: #511a7f;
  --sky-bg-day: linear-gradient(180deg, rgba(231,95,122,1) 0%, rgba(255,177,104,1) 83%);
  --tree-trunk: #3b3853;
  --tree: #78177b;
  --sun: linear-gradient(180deg, rgba(255,219,156,1) 0%, rgba(254,195,87,1) 53%);
  --day-night: #6c528cb3;
}
body {
  display: flex;
  justify-content: center;
  align-items: center;
  background-color: var(--wrapper-bg);
  transition: .2s linear;
}
input {
  display: none;
}

.toggle-wrapper {
  position: relative;
  cursor: pointer;
  border-radius: 120px;
  width: 550px;
  height: 200px;
  background: #fff;
  overflow: hidden;
  background: var(--sky-bg-night);
  
  &:before {
    content: "";
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(180deg, rgba(231,95,122,1) 0%, rgba(255,177,104,1) 83%);
    opacity: 0;
    transition: 1s;
    border-radius: 120px;
    overflow: hidden;
  }
}

input#switch:checked + *:before {
    opacity: 1;
}

.hills { 
  position: relative;
  display: flex;
  width: 720px; 
  bottom: -150px;
  left: -40px;
}

.hill-left {
  position: relative;
  z-index: 2;
  width: 380px;
  height: 120px;
  border-radius: 100%;
  background: var(--hill-left);
  top:  -6px;
  left: -10px;
  transform: rotate(8deg);
}

.hill-right {
  position: relative;
  z-index: 1;
  width: 340px;
  height: 150px;
  border-radius: 100%;
  background: var(--hill-right);
  left: -80px;
}

.tree-left {
  position: absolute;
  z-index: 5;
  left: 100px;
  bottom: -40px;
  bottom: -40px;
}

.tree-left .trunk {
  z-index: 3;
  height: 200px;
  width: 16px;
  background: var(--tree-trunk);
  border-radius: 100% 100% 0 0;
}

.branch {
  background: var(--tree-trunk);
  position: relative;
}

.branch:nth-child(1) {
  width: 10px;
  height: 70px;
  top: 46px;
  left: -10px;
  border-radius: 100%;
  transform: rotate(-22deg);
  &:before {
    content:"";
    position: absolute;
    width: 10px;
    height: 44px;
    left: -21px;
    top: 26px;
    border: 10px solid var(--tree-trunk);
    border-color:  transparent  var(--tree-trunk) transparent transparent;
    border-radius: 60%;
    transform: rotate(10deg);
  }
}

.branch:nth-child(2) {
  width: 10px;
  height: 60px;
  top: -46px;
  left: 16px;
  border-radius: 100%;
  transform: rotate(22deg);
  &:after {
    content:"";
    position: absolute;
    width: 10px;
    height: 56px;
    left: 2px;
    top: 20px;
    border: 10px solid var(--tree-trunk);
    border-color:  transparent  transparent transparent var(--tree-trunk);
    border-radius: 60%;
    transform: rotate(-11deg);
  }
}

.tree-left .tree {
  position: absolute;
  left: -50px;
  top: -10px;
  width: 120px;
  height: 120px;
  z-index: -1;
  background: var(--tree);
  border-radius: 63% 37% 31% 69% / 60% 74% 26% 40% ;
  transform: rotate(40deg);
  
  &:before {
    content:"";
    position: absolute;
    left: -50px;
    top: -50px;
    width: 120px;
    height: 120px;
    z-index: -1;
    background: var(--tree);
    border-radius: 63% 37% 31% 69% / 60% 74% 26% 40% ;
  }
}

.tree-right { 
  position: relative;
  left: 370px;
  top: 40px;
}

.tree-back {
  position: absolute;
  z-index: 2;
  width: 36px;
  height: 80px;
  border-radius: 80%;
  background: var(--tree);
  top: 30px;
  border-bottom: 100px;
  border-color: var(--tree);
  
  .trunk {
    position: absolute;
    top: 78px;
    background: var(--tree);
    width: 10px;
    height: 23px;
    left: 14px;
  }
}

.tree-front {
  position: absolute;
  z-index: 3;
  width: 54px;
  height: 120px;
  border-radius: 80%;
  background: var(--tree);
  top: -6px;
  left: 70px;
  border-bottom: 100px;
  border-color: var(--tree);
}
.tree-front .trunk {
  position: absolute;
  z-index: 2;
  top: 120px;
  background: var(--tree-trunk);
  width: 12px;
  height: 28px;
  left: 21px;
  border-radius: 4px;
  &:before {
    content:"";
    position: absolute;
    width: 12px;
    height: 30px;
    background: var(--tree-trunk);
    left: -2px;
    top: -2px;
    border-radius: 4px;
    transform: rotate(2deg);
    transform: skewx(-10deg);
  }

  &:after {
    content:"";
    position: absolute;
    top: 23px;
    left: -4px;
    width: 14px;
    height: 6px;
    background: var(--tree-trunk);
    border-radius: 100%;
  }
}
.moon {
  position: absolute;
  background-color: transparent;
  width: 100px;
  height: 100px;
  border-radius: 50%;
  box-shadow: inset -25px -17px 0 3px #fff;
  left: 190px;
  transform: translatey(40px);
  transition: all 0.6s ease-out 0.3s;
  transition-duration: 0.8s;
  
  .switch & {
    transform: translatey(160px);
    transition: all 0.5s ease-out 0.3s;
    transition-duration: 0.8s;
  }
}

.stars {
  position: absolute;
  right: 124px;
  transform: translatey(50px);
  transition: all 0.6s ease-in 0.3s;
  
  .switch & {
    transform: translatey(-80px);
    transition: all 0.6s ease-in 0.3s;
  }
}

.star { 
  position: relative;
  background: #fff; 
}

.big-star .vertical {
  width: 12px;
  height: 12px;

  &:before {
    content:"";
    position: absolute;
    top: -12px;
    width: 0;
    height: 0;
    border-right: 6px solid transparent;
    border-left: 6px solid transparent;
    border-bottom: 12px solid #fff;
  }
  &:after {
    content: "";
    position: absolute;
    top: 12px;
    border-right: 6px solid transparent;
    border-left: 6px solid transparent;
    border-top: 12px solid #fff;
  }
}

.big-star .horizontal {
  position: relative;
  transform: rotate(90deg);
  left: 6px;
  top: -6px;
  
  &:before {
     content:"";
     position: absolute;
     top: -12px;
     width: 0;
     height: 0;
     border-right: 6px solid transparent;
     border-left: 6px solid transparent;
     border-bottom: 12px solid #fff;
   }
   &:after {
     content: "";
     position: absolute;
     top: 12px;
     border-right: 6px solid transparent;
     border-left: 6px solid transparent;
     border-top: 12px solid #fff;
   }
}

.small-star { 
  top:-36px;
  left: 24px;
  width: 8px;
  height: 8px;
}

.small-star .vertical {
  &:before {
    content:"";
    position: absolute;
    top: -8px;
    width: 0;
    height: 0;
    border-right: 4px solid transparent;
    border-left: 4px solid transparent;
    border-bottom: 8px solid #fff;
  }
  &:after {
    content: "";
    position: absolute;
    top: 8px;
    border-right: 4px solid transparent;
    border-left: 4px solid transparent;
    border-top: 8px solid #fff;
  }
}

.small-star .horizontal {
  position: relative;
  transform: rotate(90deg);
  top: 4px;
  left: 4px;
  
  &:before {
     content:"";
     position: absolute;
     top: -8px;
     width: 0;
     height: 0;
     border-right: 4px solid transparent;
     border-left: 4px solid transparent;
     border-bottom: 8px solid #fff;
   }
   &:after {
     content: "";
     position: absolute;
     top: 8px;
     border-right: 4px solid transparent;
     border-left: 4px solid transparent;
     border-top: 8px solid #fff;
   }
}

.sun {
  position: absolute;
  z-index: 0;
  width: 150px;
  height: 150px;
  border-radius: 50%;
  background: var(--sun);
  left: 240px;
  top: 160px;
  box-shadow: 8px 8px 54px 12px rgba(255,214,150,0.97);
  transition: all 0.8s ease-in 0.3s;
  transform: translatey(20px);
  
  .switch & {
    transition: all 0.8s ease-out 0.3s;
    transform: translatey(-40px);
  }
}

.day-night {
  position: absolute;
  z-index: 6;
  width: 200px;
  height: 200px;
  border-radius: 50%;
  background-color: var(--day-night);
  overflow: hidden;
  transition: all 0.8s ease-in;
  transform: translatex(0);
  backdrop-filter: blur(6px);
  
  .switch & {
    transform: translatex(350px);
  }
}
@media screen and (max-width: 550px) {
  .toggle-wrapper {
    transform:scale(0.5);
  }
}
View Compiled
document.addEventListener('DOMContentLoaded', function () {
  var checkbox = document.querySelector('input[type="checkbox"]');
  
  checkbox.addEventListener('change', function () {
    document.documentElement.classList.toggle('switch');
  });
});

External CSS

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