:checked css not working - html

Question

I have a product listing little square thing, when I click it ( it's a label ) it should tick the box and it does but it should make the border green and hold it but it doesn't I have this:
.product {
width: 100%;
background: #fff;
border: 4px solid #fff;
border-radius: 4px;
margin-bottom: 20px;
box-shadow: 0 2px 3px #ddd;
text-align:center;
padding-bottom: 15px;
cursor: pointer;
-webkit-transition: all .3s ease;
-moz-transition: all .3s ease;
-o-transition: all .3s ease;
-ms-transition: all .3s ease;
transition: all .3s ease;
a {
color: #d6d6d6;
line-height: 25px;
border-radius: 100%;
background: #f2f2f2;
width: 25px;
height: 25px;
display: block;
position: absolute;
margin: 10px;
-webkit-transition: all .3s ease;
-moz-transition: all .3s ease;
-o-transition: all .3s ease;
-ms-transition: all .3s ease;
transition: all .3s ease;
&:hover {
background: #e2e1e1;
color: #333;
text-decoration: none
}
}
img {
width: 80%;
margin: 15px auto;
pointer-events: none;
}
span {
display: block;
&.brand {
color: #cdcfd2;
font-size: 13px;
font-weight: 300;
}
&.name {
color: #232f3e;
font-size: 16px;
font-weight: 600;
}
}
&:hover {
border: 4px solid #d9dce1;
box-shadow: none;
}
}
and this works great it's .less my html looks like this:
<div class="col-md-2">
<label for="product_id" name="product_id" class="product">
i
<div class="position">
<input type="checkbox" class="checkbox" name="product_id" id="product_id">
</div>
<img src="assets/images/products/image.jpg">
<span class="brand">Brand</span>
<span class="name">Product</span>
</label>
How do I would I apply the suggestions in this checked: example?
input[type=checkbox]:checked + label { }
It looks pretty simple but when I add it it doesn't work all I want is the .product border to be green instead of grey when it's selected
I know I can use js but I don't want to css should do it.

Answer 1

+ is an adjacent sibling selector, meaning it matches the element after it based on the selector. Simply add a label tag after your <input type="checkbox"> tag.
.product {
width: 100%;
background: #fff;
border: 4px solid #fff;
border-radius: 4px;
margin-bottom: 20px;
box-shadow: 0 2px 3px #ddd;
text-align: center;
padding-bottom: 15px;
cursor: pointer;
-webkit-transition: all .3s ease;
-moz-transition: all .3s ease;
-o-transition: all .3s ease;
-ms-transition: all .3s ease;
transition: all .3s ease;
}
.product a {
color: #d6d6d6;
line-height: 25px;
border-radius: 100%;
background: #f2f2f2;
width: 25px;
height: 25px;
display: block;
position: absolute;
margin: 10px;
-webkit-transition: all .3s ease;
-moz-transition: all .3s ease;
-o-transition: all .3s ease;
-ms-transition: all .3s ease;
transition: all .3s ease;
}
.product a:hover {
background: #e2e1e1;
color: #333;
text-decoration: none;
}
.product img {
width: 80%;
margin: 15px auto;
pointer-events: none;
}
.product span {
display: block;
}
.product span.brand {
color: #cdcfd2;
font-size: 13px;
font-weight: 300;
}
.product span.name {
color: #232f3e;
font-size: 16px;
font-weight: 600;
}
.product:hover {
border: 4px solid #d9dce1;
box-shadow: none;
}
input[type=checkbox]:checked + label {
color: red;
}
<div class="col-md-2">
<label for="product_id" name="product_id" class="product">
i
<div class="position">
<input type="checkbox" class="checkbox" name="product_id" id="product_id">
<label for="product_id">label</label>
</div>
<img src="assets/images/products/image.jpg">
<span class="brand">Brand</span>
<span class="name">Product</span>
</label>

Answer 2

to work "+" tags need to go one by one
css:
input[type=checkbox]:checked + label { }
html:
<input type="checkbox" id="id"><label for="id">...</label>
input[type=checkbox]:checked + label {
background-color: red;
}
<input type="checkbox" id="id">
<label for="id">Test</label>

Answer 3

For anyone struggling
The input and the element that you're modifying need to be directly next to the each other, for the :checked rule to work.
#hidden {
display: none;
height: 100px;
background: red;
}
:checked + #hidden {
display: block;
}
<input type="checkbox" id="my_checkbox" style="display:none;">
<!-- NEED TO BE NEXT TO EACH OTHER ^ -->
<div id="hidden"></div>
<label for="my_checkbox">Show/hide</label>