In the following code there:

.bx-spl-line.bx-spl-l1 .bx-spl-cell.bx-spl-c1 {

        -webkit-flex: 1 1 70%; 

        flex:  1 1 70%;

          width: 70%;

    }

      .bx-media-phone .bx-spl-line.bx-spl-l1 .bx-spl-cell.bx-spl-c1 {

          text-align: center;

      }

      .bx-spl-line.bx-spl-l1 .bx-spl-cell.bx-spl-c2 {

        -webkit-flex: 0 0 30%; 

        flex:  0 1 30%;

          -webkit-justify-content: center;

        justify-content: center;

          width: 30%;

    }

In the selected parts change the number of percents to other proportions.