To perform this:
I removed the line: $table->width = '100%';
I added the line: $table->attributes['class'] = 'sessionlisttable'; on renderer.php
And I added the line: .sessionlisttable { width: 100%; } on styles.css

But the width of the table is Not 100% on the output page. Can you please check what I did wrong. I looked into moodle api and into moodle forums and I see that is how it is done, but still I did not get the desired output.