Input type checkbox values - html

Question

I am looking at this w3schools checkbox demo
I notice that input doesn't get checked value when checked. Is this valid html?
I tried using this with php forms and the value if "on" when checked.
.container {
display: block;
position: relative;
padding-left: 35px;
margin-bottom: 12px;
cursor: pointer;
font-size: 22px;
-webkit-user-select: none;
-moz-user-select: none;
-ms-user-select: none;
user-select: none;
}
/* Hide the browser's default checkbox */
.container input {
position: absolute;
opacity: 0;
cursor: pointer;
}
/* Create a custom checkbox */
.checkmark {
position: absolute;
top: 0;
left: 0;
height: 25px;
width: 25px;
background-color: #eee;
}
/* On mouse-over, add a grey background color */
.container:hover input~.checkmark {
background-color: #ccc;
}
/* When the checkbox is checked, add a blue background */
.container input:checked~.checkmark {
background-color: #2196F3;
}
/* Create the checkmark/indicator (hidden when not checked) */
.checkmark:after {
content: "";
position: absolute;
display: none;
}
/* Show the checkmark when checked */
.container input:checked~.checkmark:after {
display: block;
}
/* Style the checkmark/indicator */
.container .checkmark:after {
left: 9px;
top: 5px;
width: 5px;
height: 10px;
border: solid white;
border-width: 0 3px 3px 0;
-webkit-transform: rotate(45deg);
-ms-transform: rotate(45deg);
transform: rotate(45deg);
}
<h1>Custom Checkboxes</h1>
<label class="container">One
<input type="checkbox" checked="checked">
<span class="checkmark"></span>
</label>
<label class="container">Two
<input type="checkbox">
<span class="checkmark"></span>
</label>
<label class="container">Three
<input type="checkbox">
<span class="checkmark"></span>
</label>
<label class="container">Four
<input type="checkbox">
<span class="checkmark"></span>
</label>

Answer 1

The value of a checkbox is whatever the value attribute says it is with (in the case of checkboxes) on as the default.
Its checked status (available via the checked property in JS) determines if it will be a successful control (i.e. appear in the submitted form data at all) or not.

Answer 2

Just remove checked="checked" so that that initial wont be checked
/* When the checkbox is checked, add a blue background */
.container input:checked~.checkmark {
background-color: #2196F3;
}
/* Create the checkmark/indicator (hidden when not checked) */
.checkmark:after {
content: "";
position: absolute;
display: none;
}
/* Show the checkmark when checked */
.container input:checked~.checkmark:after {
display: block;
}
/* Style the checkmark/indicator */
.container .checkmark:after {
left: 9px;
top: 5px;
width: 5px;
height: 10px;
border: solid white;
border-width: 0 3px 3px 0;
-webkit-transform: rotate(45deg);
-ms-transform: rotate(45deg);
transform: rotate(45deg);
}
<h1>Custom Checkboxes</h1>
<label class="container">One
<input type="checkbox">
<span class="checkmark"></span>
</label>
<label class="container">Two
<input type="checkbox">
<span class="checkmark"></span>
</label>
<label class="container">Three
<input type="checkbox">
<span class="checkmark"></span>
</label>
<label class="container">Four
<input type="checkbox">
<span class="checkmark"></span>
</label>