You can achieve this by using custom styling.
Structurally, a groupbox consists of a container, within this container there are 2 other containers: header and body. You can use flex-box to align the header left and content right and apply possible width to the body:
==== HTML =====
<div class="mx-groupbox">
<div class="mx-groupbox-header">
//GROUPBOX HEADER
</div>
<div class="mx-groupbox-body">
//GROUPBOX CONTENT
</div>
</div>
===== CUSTOM SCSS =====
.mx-groupbox {
display: flex;
flex-direction: row;
.mx-groupbox-body {
// possible width properties
}
}
===== RESULT =====
------------------------------------------
| | |
| | |
| HEADER | CONTENT |
| | (with possible fixed width) |
| | |
------------------------------------------
Hope this helps!