Applying custom styling to required asterisk(*) is quite difficult if there isn't any class name assigned to it.
Generic solutions like below don't always work and tend to interfere with other elements matching the condition.(specially when displaying columns vertically).
Can you please make some modifications in the library to have css class assigned to it?
Code.sv_matrix_cell_header span:nth-child(2){
color: red;
font-size: 15px;
}
.sv_matrix_cell span:nth-child(2){
color: red;
font-size: 15px;
}