If you continue to experience any issues please do not hesitate to contact me.

Hello Gabriel, 

The CSS files, responsible for the stilling of the Infragistics Controls could be found in the ig_res folder, that is created when an Infragistics Control is initially added.
The CSS file related to the WebDataMenu is ig_datamenu.css. It could be accessed and modified.   

In order to customize the main menu container named as default as id=”WebDataMenu 1” a CSS class igdm_ControlVertical  is available. Here is a code snippet, where the border, border-radius and height are manually added to the CSS class : 

.igdm_ControlVertical

{
background-color: #EFEFEF;
background-repeat: repeat-x;
background-position: top;
background-image: url(images/igdm_controlbackground.png);
font-family: Verdana,Arial,Lucida Grande,Lucida Sans Unicode,Lucida,Helvetica,Sans-serif;
border-style: none;
border-width: 0px;
white-space: nowrap;
overflow: hidden;
cursor: default;
border: 2px solid blue;
border-radius: 5px 5px 5px 5px;
height: 100px;
}