How to Create a Half-Circle with CSS Using a Single Div?

Creating a Half Circle with CSS

Question:

How do you create a half-circle using only CSS, with a single div element and without relying on external tools like SVG or graphics APIs?

Answer:

Achieving a half-circle effect with CSS can be accomplished by leveraging border properties. To do this:

1. Use border-top-left-radius and border-top-right-radius to round the corners of the box based on its height and any added borders. For example:

border-top-left-radius: 110px;  // Height + Border
border-top-right-radius: 110px; // Height + Border

2. Add borders to the top, right, and left sides of the box. Set the border-bottom to zero to remove the bottom border.

border: 10px solid gray;
border-bottom: 0;

This combination of rounded corners and borders creates a half-circle shape.

Example:

<code class="css">.half-circle {
    width: 200px;
    height: 100px;
    border-top-left-radius: 110px;
    border-top-right-radius: 110px;
    border: 10px solid gray;
    border-bottom: 0;
}</code>

Alternative Method:

An alternative approach is to use box-sizing: border-box, which calculates the width and height of the box including borders and padding. This way, you can specify the height as exactly half of the width:

<code class="css">.half-circle {
    width: 200px;
    height: 100px;
    border-top-left-radius: 100px;
    border-top-right-radius: 100px;
    border: 10px solid gray;
    border-bottom: 0;

    box-sizing: border-box;
}</code>

Both methods can achieve the desired half-circle effect using purely CSS techniques.

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