You can change the shape of a button in CSS by using the `border-radius` property. The `border-radius` property is used to add rounded borders to an element, which can be used to make a button shape circular or oval.
For example, if you have a button with the id “myButton”, you could make it round by applying a large value of `border-radius` as shown below:
```
#myButton {
border-radius: 50%; /* This will make the button round */
width: 100px; /* Define a specific width */
height: 100px; /* Define a specific height */
}
```
If you want to make the button elliptical, you can set different values for horizontal and vertical radius like:
```
#myButton {
border-radius: 50% / 30%; /* This will make the button elliptical */
width: 100px; /* Define a specific width */
height: 50px; /* Define a specific height */
}
```
And if you want to make the button into a rounded rectangle (pill-shaped), you can use a large border-radius:
```
#myButton {
border-radius: 25px; /* This will make the button pill-shaped with rounded corners */
padding: 10px 20px; /* Add some padding for text */
}
```
Remember to also define a specific width and height for the button when crafting certain shapes, like circles or ellipses.
