.container {
  --input-focus: #2d8cf0;
  --input-out-of-focus: #111;
  --bg-color: #111;
  --bg-color-alt: #7e7e7e;
  --main-color: #fefefe;
  position: relative;
  cursor: pointer;
}

.container input {
  position: absolute;
  opacity: 0;
}

.checkmark {
  width: 30px;
  height: 30px;
  position: relative;
  top: 0;
  left: 0;
  border: 2px solid var(--main-color);
  border-radius: 5px;
  box-shadow: 4px 4px var(--main-color);
  background-color: var(--input-out-of-focus);
  transition: all 0.3s;
}

.container input:checked ~ .checkmark {
  background-color: var(--input-focus);
}

.checkmark:after {
  content: "";
  width: 7px;
  height: 15px;
  position: absolute;
  top: 2px;
  left: 8px;
  display: none;
  border: solid var(--main-color);
  border-width: 0 2.5px 2.5px 0;
  transform: rotate(45deg);
}

.container input:checked ~ .checkmark:after {
  display: block;
}