Discussion on the small problems in JS and CSS loading _ basic knowledge

In the JS script, there are two window.onload

Copy Code code as follows:

Window.onload = function () {
Alert ("AAA");
};

Window.onload = function () {
Alert ("BBB");
};

Will only execute one, this is the set of its own function, it is noteworthy that the pop-up is not AAA, but BBB, executed is the last

In CSS files, in CSS styles

Copy Code code as follows:

#checks {
Padding-left:20px;padding-top:16px;margin:auto;
}
#checks {
Padding-left:80px;padding-top:38px;margin:auto;
}

is also the back of the style entry into force, if the second padding-left is removed, use the first padding-left

In HTML tags

<TD style= "Padding-left:10px;padding-top:8px;margin:auto style=" Padding-left:20px;padding-top:16px;margin: auto; " ></td>

This is the first one to take effect, and the top two different

I would like someone to help explain ...