As far as I know, there's no tutorial for this.

To do this, you have to use CSS. You can directly type the CSS in the settings of the form or can reference a CSS style sheet in the settings of the form, Advanced part.

To make the corners rounded (for the input controls), you can use this CSS :

input, select, textarea, .ms-inputBox, .ip-container, .ip-item span {

     -moz-border-radius: 5px;

     -webkit-border-radius: 5px;

     border-radius: 5px;

}

Hope this helps