Arc-theme: Graphical glitch in elementaryOS Photos' app

[n1c0saurio]

Perfectly described here.

I have the same issue in Loki (gnome 3.18) with Arc theme version 20161005 (manually installed).

[wilsenhc]

I'm experiencing this exact same issue with pantheon-photos

[ghost]

pantheon-photos IS elementary OS "Photos".
Adding this snippet from the elementary theme (gtk3/apps.css) to both gtk.css and gtk-dark.css in the gtk-3.18 subfolder solved it for me for all Arc (based) themes. I'm on elementary OS 0.4.1 with GTK+ 3.18.9. I placed the snippet after the first closing curly bracket.

... }

    /**********
     * Photos *
     *********/

    .checkerboard-layout {
        background-color: #383e41;
        background-image:
            linear-gradient(
                45deg,
                alpha (
                    #000,
                    0.1
                ) 25%,
                transparent 25%,
                transparent 75%,
                alpha (
                    #000,
                    0.1
                ) 75%,
                alpha (
                    #000,
                    0.1
                )
            ),
            linear-gradient(
                45deg,
                alpha (
                    #000,
                    0.1
                ) 25%,
                transparent 25%,
                transparent 75%,
                alpha (
                    #000,
                    0.1
                ) 75%,
                alpha (
                    #000,
                    0.1
                )
            );
        background-size: 24px 24px;
        background-position: 0 0, 12px 12px;
    }

    .checkboard-layout .item {
        background-color: #eee;
    }

    /* end Photos snippet */