In one of the reply to the query for fixed first column of matrix dynamic you have given this css.
table.sv_q_matrix_dynamic {
display: block;
width: calc(100% - 150px) !important;
overflow-x: scroll;
margin-left: 150px;
}
table.sv_q_matrix_dynamic tr>th:first-child {
position: absolute;
width: 150px;
margin-left: -150px;
margin-top: 11px;
border-bottom: 1px solid rgb(231, 231, 231);
}
It works fine with the default theme but does not work in the modern theme. So, if i have to fixed first column of matrix dropdown in modern theme what needs to be done.