private void dataGridView1_RowPrePaint(object sender, DataGridViewRowPrePaintEventArgs e)
        {
            if (e.RowIndex < 0 || dataGridView1.Rows[e.RowIndex].IsNewRow) return;
            var dt = DateTime.Now;
            dt = new DateTime(dt.Year, dt.Month, dt.Day, 0, 0, 0);

            if (((DateTime)dataGridView1.Rows[e.RowIndex].Cells["Срок до"].Value).CompareTo(dt) < 0)
                dataGridView1.Rows[e.RowIndex].DefaultCellStyle.BackColor = Color.Red;
        }