To create a custom template with your own logo or styling, download a thumbnail as SVG and edit it with a vector graphics editor (I use Inkscape).
Elements in your SVG with the following IDs will be automatically replaced with data from start.gg:
char1_portraitchar2_portraitchar1_zoomedchar2_zoomedchar1_muralchar2_muralp1_sponsoredp2_sponsoredp1p2roundeventphase