copy the following CSS into the bottom of your stylesheet
/* ADDON: REMOVE SIDEBAR IMAGE */
.side:before { display: none }
.side .titlebox h1.redditname { top: calc(308px - 80px) }
.titlebox .fancy-toggle-button { top: calc(314px - 80px) }
.titlebox span.subscribers { top: calc(336px - 80px) }
#search { top: calc(384px - 80px) }
.submit .morelink { top: calc(442px - 80px) }
.side { margin-top: calc(282px - 80px) }
.comments-page .side .linkinfo { top: calc(494px - 80px) }
.comments-page .side { margin-top: calc(400px - 80px) }
.search-page .side .titlebox h1.redditname { top: calc(256px - 80px) }
.search-page .titlebox .fancy-toggle-button { top: calc(276px - 80px) }
.search-page .titlebox span.subscribers { top: calc(300px - 80px) }
.search-page .morelink { top: calc(350px - 80px) }
.search-page .side { margin-top: calc(234px - 80px) }
/* END ADDON */