To create a gradient button with a hover effect using CSS3, you can use the following code:

In this example, the button has a gradient background using the linear-gradient property, which creates a gradient that goes from #fca311 to #ffba08. The color property sets the text color to white, while font-size, font-weight, border, border-radius, and padding properties are used to style the button.

The transition property sets the transition effect when the button is hovered over. In this case, the transform property is used to move the button up by 3 pixels and the box-shadow property adds a subtle shadow effect to the button.

When the button is hovered over, the :hover pseudo-class is applied, which triggers the transition effect.

You can modify the CSS properties to customize the gradient and hover effects to your liking.