node-red/packages/node_modules/@node-red/editor-client/src/sass/ace.scss

.ace_gutter {
    border-top-left-radius: 4px;
    border-bottom-left-radius: 4px;
}
.ace_scroller {
    border-top-right-radius: 4px;
    border-bottom-right-radius: 4px;
}

#event-log-editor {
    .ace_scroller {
        background: #444;
        color: #dd9;
    }
    .ace_active-line {
        background: #666 !important;
    }
    .ace_selection {
        background: #999 !important;
    }
}