Изменить border у checkbox

.styled-checkbox {
  position: absolute; // take it out of document flow
  opacity: 0; // hide it
 
  & + label {
    position: relative;
    cursor: pointer;
    padding: 0;
  }
 
  // Box.
  & + label:before {
    content: '';
    margin-right: 10px;
    display: inline-block;
    vertical-align: text-top;
    width: 20px;
    height: 20px;
    background: white;
  }
 
  // Box hover
  &:hover + label:before {
    background: #f35429;
  }
  
  // Box focus
  &:focus + label:before {
    box-shadow: 0 0 0 3px rgba(0, 0, 0, 0.12);
  }
 
  // Box checked
  &:checked + label:before {
    background: #f35429;
  }
  
  // Disabled state label.
  &:disabled + label {
    color: #b8b8b8;
    cursor: auto;
  }
 
  // Disabled box.
  &:disabled + label:before {
    box-shadow: none;
    background: #ddd;
  }
 
  // Checkmark. Could be replaced with an image
  &:checked + label:after {
    content: '';
    position: absolute;
    left: 5px;
    top: 9px;
    background: white;
    width: 2px;
    height: 2px;
    box-shadow: 
      2px 0 0 white,
      4px 0 0 white,
      4px -2px 0 white,
      4px -4px 0 white,
      4px -6px 0 white,
      4px -8px 0 white;
    transform: rotate(45deg);
  }
}
 
// Demo-only styles
// --------------
 
html {
  background: lightgray;
}
 
body {
  font-family: 'Source Sans Pro', sans-serif;
}
 
.unstyled {
  margin: 0;
  padding: 0;
  list-style-type: none;
}
 
li {
  margin: 20px 0;
}
 
.centered {
  width: 300px;
  margin: auto;
}
 
.title {
  text-align: center;
  color: rgb(69, 113, 236);
}