You just need to add the following two lines in your theme’s style.css.

.textwidget ul {margin-left:15px; }
.textwidget ul li {list-style-type: circle; margin-left: 10px; }

You can change list-style-type to square or disc.

Written by Shengdong Zhao

Shen is an Associate Professor in the Computer Science Department, National University of Singapore (NUS). He is the founding director of the NUS-HCI Lab, specializing in research and innovation in the area of human computer interaction.