Divi buttons normally scale with text, which can look crappy. Set a minimum width with this CSS - buttons will scale up depending on text content.

divi-button-min-size

.et_pb_button { min-width: 180px; text-align:center; }

//Or for more targeted styles, apply your own class

.your-css-class .et_pb_button { min-width: 180px; text-align:center; }