其实是新老版本的css样式差异导致 可以用beyondcompare自行对比。 老版本有问题：

/** initial setup **/
.nano {
    position : relative;
    width    : 100%;
    height   : 100%;
    overflow : hidden;
}
.nano > .nano-content {
    position      : absolute;
    overflow      : scroll;
    overflow-x    : hidden;
    top           : 0;
    right         : 0;
    bottom        : 0;
    left          : 0;
    outline: none;
    scrollbar-width: none;
}

.nano > .nano-content::-webkit-scrollbar {
    display: none;
}
.has-scrollbar > .nano-content::-webkit-scrollbar {
    display: block;
}
.nano > .nano-pane {
    background-color: #f8f8f8;
    position   : absolute;
    width      : 9px;
    right      : 0;
    top        : 0;
    bottom     : 0;
    visibility : hidden\9; /* Target only IE7 and IE8 with this hack */
    opacity    : .01;
    -webkit-transition    : .2s;
    -moz-transition       : .2s;
    -o-transition         : .2s;
    transition            : .2s;
    -moz-border-radius    : 5px;
    -webkit-border-radius : 5px;
    border-radius         : 5px;
}
.nano > .nano-pane > .nano-slider {
    background: rgba(137, 160, 179, 0.5);
    transform: translate(0px, 85.7732px);
    position              : relative;
    margin                : 0 1px;
    -moz-border-radius    : 3px;
    -webkit-border-radius : 3px;
    border-radius         : 2px;
}
.nano:hover > .nano-pane, .nano-pane.active, .nano-pane.flashed {
    visibility : visible\9; /* Target only IE7 and IE8 with this hack */
    opacity    : 0.99;
}

新版本无问题：

/** initial setup **/
.nano {
    position : relative;
    width    : 100%;
    height   : 100%;
    overflow : hidden;
}
.nano > .nano-content {
    position      : absolute;
    overflow      : scroll;
    overflow-x    : hidden;
    top           : 0;
    right         : 0;
    bottom        : 0;
    left          : 0;
}
.nano > .nano-content:focus {
    outline: thin dotted;
}
.nano > .nano-content::-webkit-scrollbar {
    display: none;
}
.has-scrollbar > .nano-content::-webkit-scrollbar {
    display: block;
}
.nano > .nano-pane {
    background : rgba(0,0,0,.25);
    position   : absolute;
    width      : 10px;
    right      : 0;
    top        : 0;
    bottom     : 0;
    visibility : hidden\9; /* Target only IE7 and IE8 with this hack */
    opacity    : .01;
    -webkit-transition    : .2s;
    -moz-transition       : .2s;
    -o-transition         : .2s;
    transition            : .2s;
    -moz-border-radius    : 5px;
    -webkit-border-radius : 5px;
    border-radius         : 5px;
}
.nano > .nano-pane > .nano-slider {
    background: #444;
    background: rgba(0,0,0,.5);
    position              : relative;
    margin                : 0 1px;
    -moz-border-radius    : 3px;
    -webkit-border-radius : 3px;
    border-radius         : 3px;
}
.nano:hover > .nano-pane, .nano-pane.active, .nano-pane.flashed {
    visibility : visible\9; /* Target only IE7 and IE8 with this hack */
    opacity    : 0.99;
}

对比图：