Define an image as the submit button, with height and width attributes:
The width attribute specifies the width of the <input> element.
Note: The width attribute is used only with <input type="image">.
Tip: Always specify both the height and width attributes for images. If height and width are set, the space required for the image is reserved when the page is loaded. However, without these attributes, the browser does not know the size of the image, and cannot reserve the appropriate space to it. The effect will be that the page layout will change during loading (while the images load).
The numbers in the table specify the first browser version that fully supports the attribute.
The width attribute is new for the <input> tag in HTML5.
|pixels||The width in pixels (e.g. width="100")|