gmail-user-style.css

/* footer */
.aeG, .pfiaof {
    display: none;
}

/* hide header logo and hamburger */
.gb_3c {
    display: none !important;
}

/* hide header settings and profile buttons */
.gb_De.gb_Be,
.gb_9d.gb_Xa.gb_Ud.gb_ce {
    display: none;
}

/* hide support, input options, etc. */
.aKh,
.aBS,
.G-Ni,
#itamenu,
#gbwa,
#lZwQje {
    display: none !important;
}

/* inbox width  */
.nH.bkL {
    max-width: 1400px;
    margin: 0 auto;
    padding: 0 20px;
}
.bkK + .nn {
    display: none;
}
.bhZ + .bkK {
    margin-left: 0;
}

/* email list */
.yO {
    background-color: transparent;
}

/* individual emails */
.zA {
    padding-top: 14px;
    padding-bottom: 14px;
    box-shadow: none;
}
.zA:hover {
    background: #fafafa;
    box-shadow: none;
}

/* other app links */
.brC-aT5-aOt-Jw {
    display: none;
}

/* search */
.gb_6e.gb_Df {
    max-width: 100%;
}
.gb_qf::placeholder {
    color: transparent !important;
}
.gb_Se {
    padding: 0 10px !important;
}

/* left sidebar */
.oy8Mbf.aeN {
    position: fixed;
    left: 0;
    margin-left: -250px;
    z-index: 100;
    transition: none;
}

.oy8Mbf.aeN:hover {
    background: #fff;
    margin-left: 0;
    box-shadow: inset -1px 0 0 0 rgba(100,121,143,0.122);
}

.oy8Mbf.aeN:hover .aj5.J-KU-Jg {
    box-shadow: inset -1px 0 0 0 rgba(100,121,143,0.122);        
}