coloring percentage part of an annulus

I intend to fill with yellow color percentage part of an annulus, that is originally blue. Here is my code together with an image of the current and desire state. Could you please help me to finish it? Thank you.

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8"/>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>hey I am a title</title>
    <style>

.c7 {
    background: darkblue;
    border-radius: 50%;
    width: 200px;
    height: 200px;
    margin: 90px;
    padding: 1px;
}

.c6 {
    background: white;
    border-radius: 50%;
    width: 150px;
    height: 150px;
    margin: 25px 25px 25px 25px;
}



    </style>
</head>
<body>



<div class="c7">
    <div class="c6"></div>
</div>



</body>
</html>

current vs desired state