How to change Checkbox UI Using Html and CSS?

Question

<input type='checkbox' name='chkbox'/>

I want to change the checkbox height and width and also background color if possible

Answer 1

You can look at this piece of code for starters.
It uses the before element to create a custom shape and hide the default checkbox for two states 'checked' and 'unchecked'

Also give a label for that corresponding checkbox so that clicking this custom shape will actually trigger the hidden default checkbox.

body {
  font-family: 'segoe ui';
  background-color: white;
  padding: 10px;
}

.space {
  height: 10px;
}

.checkbox * {
  box-sizing: border-box;
  position: relative;
  -webkit-touch-callout: none;
  -webkit-user-select: none;
  -khtml-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
}

.checkbox {
  display: inline-block;
}

.checkbox>input {
  display: none;
}

.checkbox>label {
  vertical-align: top;
  font-size: 18px;
  padding-left: 30px;
}

.checkbox>[type="checkbox"]+label:before {
  color: #777;
  content: '';
  position: absolute;
  left: 0px;
  display: inline-block;
  min-height: 20px;
  height: 20px;
  width: 20px;
  border: 2px solid #777;
  font-size: 15px;
  vertical-align: top;
  text-align: center;
  transition: all 0.2s ease-in;
  content: '';
}

.checkbox.radio-square>[type="checkbox"]+label:before {
  border-radius: 0px;
}

.checkbox.radio-rounded>[type="checkbox"]+label:before {
  border-radius: 25%;
}

.checkbox.radio-blue>[type="checkbox"]+label:before {
  border: 2px solid #ccc;
}

.checkbox>[type="checkbox"]+label:hover:before {
  border-color: lightgreen;
}

.checkbox>[type="checkbox"]:checked+label:before {
  width: 8px;
  height: 16px;
  border-top: transparent;
  border-left: transparent;
  border-color: green;
  border-width: 4px;
  transform: rotate(45deg);
  top: -4px;
  left: 4px;
}

<div class="checkbox">
  <input id="chkTest" type="checkbox" />
  <label for="chkTest">Task one</label>
  <div class="space">

  </div>

  <input id="chkTest1" type="checkbox" />
  <label for="chkTest1">Task two</label>
</div>