modification style css panel widget accordion

Hi,
sorry for my english
i’d like modify this element style

.so-widget-sow-accordion-default-257292cb1feb .sow-accordion .sow-accordion-panel .sow-accordion-panel-header{padding: 15px 30px 15px 30px;}

to
.so-widget-sow-accordion-default-257292cb1feb .sow-accordion .sow-accordion-panel .sow-accordion-panel-header{padding: 5px 30px 5px 30px;}

but i don't know where.
i try to change the css style in widget style but it doesn't function.
Thanks for your help.