Margin-top not working for <p> and <a> tag?

This issue is known as Margin Collapse and happens sometimes between top and bottom margins on block elements.

The margins of adjacent siblings are collapsed

That's why the margin doesn't work on the p tag. To make it work here an option is to use padding-top on the p tag.

And on the a tag the margin doesn't work because it's an inline element. You may need to change its display property to inline-block or block.

Try this:

#services ul li a{
    background-color: #4972ff;
    color: #fff;
    border-bottom: 3px solid #779bff;
    border-radius: 5px;
    -webkit-border-radius: 5px;
    -moz-border-radius: 5px;
    padding: 8px;
    position: relative;
    top: 10px;
}

the link tag <a> is inline block tags and it means it must be in one line beside other elements and should has a parent part that the parent part determines how much these inline-block elements should have margin top and button there's two ways to do that: convert theme to block:

#services a{
display: block;
margin-top: 8px;
}

or simply you can work with its padding

The <a> tag is an inline element and therefore cannot have a top or bottom margin. But you can solve this by applying display: inline-block; to it.