Coloring Overlapping Div Shapes Using CSS

Question

I am new to coding, and am trying to make the intersecting part of these div's a different color. My initial attempt was to create a third div with a border specification to mimic the shapes, but I cannot make it match perfectly. Below is the markup and styling, describing what I want to be a red square and blue circle overlapping, with the overlap section being purple.

.box {
    width: 200px;
    height: 200px;
    background: red;
    position: relative;
    top: 40px;
    left: -35px;
}

.shape {
    width: 250px;
    height: 250px;
    background: navy;
    border-radius: 50%;
    position: absolute;
    left: 50px;
    top: 50px;
}

#top-left {
    width: 148px;
    height: 147px;
    background: purple;
    position: absolute;
    top: 1px;
    left:2px;
    border-top-left-radius: 118px;
}

<div class="box">
    <div class="shape">
        <div id="top-left"></div>
    </div>
</div>

Is there an easier way to do this, or a way to make the top-left-border perfectly round?

Answer 1

Add overflow: hidden; to .shape. Position top-left relatively. Done!

.box {
    width: 200px;
    height: 200px;
    background: red;
    position: relative;
    top: 40px;
}
.shape {
    width: 250px;
    height: 250px;
    background: navy;
    border-radius: 50%;
    position: absolute;
    left: 75px;
    top: 50px;
    overflow: hidden;
}

#top-left {
    width: 150px;
    height: 150px;
    background: purple;
    position: relative;
    left: -25px;
}

<div class="box">
<div class="shape">
   <div id="top-left"></div>
</div>
</div>

Output :