作用同一class除第一个后都有相同特性

element+element

例:

使用 bootstrap

.dbc-button1 { position: relative;border-radius: 4px;outline:0; }

.dbc-button1-text { position: absolute;width: 1px;height: 1px;padding: 0;margin: -1px;overflow: hidden;clip: rect(0, 0, 0, 0);border: 0; }

.dbc-button1-line { background-color: #fff;display: block;width: 22px;height: 2px;border-radius: 1px; }

.dbc-button1-line + .dbc-button1-line { margin-top: 4px; }

@media(max-width:767px){

   .dbc-button1 {background: #F7B400;}

   .dbc-button1 { padding: 8px 7px;margin-top: 0px !important; margin-right: 0px !important; margin-bottom: 0px !important; border: none; }

   .dbc-button1:hover, .dbc-button1:focus {background: #F5AF33 !important;}

}

<button type="button" class="dbc-button1">

            <span class="dbc-button1-text">Toggle navigation</span>

            <span class="dbc-button1-line"></span>

            <span class="dbc-button1-line"></span>

            <span class="dbc-button1-line"></span>

        </button>