Customizations for Mariana and One Dark themes in Atom

styles.less

// For use with Mariana (or One Dark) theme and the One Dark UI theme
.theme-one-dark-ui {
    atom-pane .item-views {
        border-top: 5px solid #1a1f23;
        // border-top: 5px solid #519fee;

        &:empty { border: 0; }
    }

    atom-pane-axis > atom-pane.active .tab.active:before,
    atom-pane-container > atom-pane.pane .tab.active:before,
    atom-pane .tab-bar .tab.active {
        background-color: #1a1f23 !important;

        // &[data-type$="Editor"]::before {
        //     display: none;
        // }
    }

    // Projects sidebar header
    atom-pane .inset-panel .tab[data-type="TreeView"] {
        background: transparent !important;
    }

    atom-text-editor {
        background-color: rgba(0, 0, 0, 0.04);
        text-shadow: 0 0 1px rgba(0, 0, 0, 0.6);

        .invisible-character {
            color: rgba(255, 255, 255, 0.1);
            text-shadow: none;
        }

        .line.cursor-line { background: rgba(0, 0, 0, 0.4); }

        .selection .region { background: black; }

        .gutter {
            color: rgba(255, 255, 255, .5);
            background: rgba(0, 0, 0, 0.02);
            // text-shadow: 0 0 3px #000;

            &:last-child {
                background-image: linear-gradient(
                    to right,
                    rgba(0, 0, 0, 0.3), rgba(0, 0, 0, 0.04)
                );
                width: 15px;
            }

            .line-number {
                padding-left: 1em;

                &.cursor-line {
                    color: rgba(255, 255, 255, 1);
                    background-color: rgba(0, 0, 0, 0.6);
                }
            }
        }
    }
}

So pretty.