Make GMail's design less horrendous using Stylebot

stylebot.css

#gb {
    background-color: #4285f4;
    box-shadow: 0 0 4px rgba(0,0,0,.14), 0 4px 8px rgba(0,0,0,.28);
}

.zA.yO {
    background-color: white;
    box-shadow: 0 0 4px rgba(0,0,0,.14);
}

div.aeG {
    display: none;
}

div.gb_fa.gb_f {
    background-color: transparent;
    border: none;
    width: 46px;
}

div.gb_ga {
    display: none;
}

div.nH.ar4.z, div.nH.ar4.B {
    margin-left: auto;
    margin-right: auto;
    max-width: 840px;
    padding-right: 72px;
}

div.nH.ar4.z img, div.nH.ar4.B img {
    max-width: 100% ;
}

img.gb_ma.gb_ia {
    display: none;
}

To get the text color to be white in the header, and to set the background to the gray color, I used GMail's built-in themes and selected Dusk. That's not part of my custom CSS.

To collapse the left-hand navigation menu, click the hamburger icon at the top left.