很实用的几个css小技巧

.triangle{border:solid 10px transparent;width:0}
.triangle.bottom{border-top-color:green}
.triangle.top{border-bottom-color:green}
.triangle.left{border-right-color:green}
.triangle.right{border-left-color:green}

p:first-letter{
  float:left;
  color:green;
  font-size:30px;
}

p:first-letter{
   text-indent:20px
}

input::-webkit-input-placeholder{
  color: green;
  background-color: #F9F7F7;
  font-size: 14px;
}
input::-moz-input-placeholder{
  color: green;
  background-color: #F9F7F7;
  font-size: 14px;
}
input::-ms-input-placeholder{
  color: green;
  background-color: #F9F7F7;
  font-size: 14px;
}

<div class="wrap">
  <div class="ribbon">
    <a href="#">Fork me on GitHub</a>
  </div>
</div>

.wrap{
  width: 160px;
  height:160px;
  overflow:hidden;
  position: relative;
  background-color: #f3f3f3;
}
.ribbon{
  background-color: #a00;
  overflow: hidden;
  white-space: nowrap;
  position: absolute;
  /* shadom */
  -webkit-box-shadow: 0 0 10px #888;
  -moz-box-shadow: 0 0 10px #888;
  box-shadow: 0 0 10px #888;
  /* rotate */
  -webkit-transform: rotate(-45deg);
  -moz-transform: rotate(-45deg);
  -ms-transform: rotate(-45deg);
  -o-transform: rotate(-45deg);
  transform: rotate(-45deg);
  /* position */
  left: -50px;
  top: 40px;
}
.ribbon a{
  border: 1px solid #faa;
  color: #fff;
  display: block;
  font: bold 81.25% 'Helvetica Neue', Helvetica, Arial, sans-serif;
  margin: 1px 0;
  padding: 10px 50px;
  text-align: center;
  text-decoration: none;
  /* shadow */
  text-shadow: 0 0 5px #444;
}

// 注意只能修改这两个属性 字体颜色 选中背景颜色
element::selection{
  color: green;
  background-color: pink;
}
element::-moz-selection{
  color: green;
  background-color: pink;
}

.loading:after {
    display: inline-block;
    overflow: hidden;
    vertical-align: bottom;
    content: '\2026';
    -webkit-animation: ellipsis 2s infinite;
}
@-webkit-keyframes ellipsis {
    from {
        width: 2px;
    }
    to {
        width: 15px;
    }
}

@-webkit-keyframes dancing-dots-jump {  
  0% { top: 0; }  
  55% { top: 0; }  
  60% { top: -10px; }  
  80% { top: 3px; }  
  90% { top: -2px; }  
  95% { top: 1px; }  
  100% { top: 0; }  
}    
span.jumping-dots > span {  
  -webkit-animation: dancing-dots-jump 1800ms infinite;  
  padding: 1px;  
  position: relative;  
}    
span.jumping-dots > span:nth-child(2) {  
  -webkit-animation-delay: 100ms;  
}  
span.jumping-dots > span:nth-child(3) {  
  -webkit-animation-delay: 300ms;  
}

{color: transparent;
text-shadow:0 0 2px rgba(0,0,0,.5);}

/* 宽度固定，适合单行显示... */
{
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}
/* 宽度不固定，适合多行以及移动端显示 */
{
    overflow: hidden;
    text-overflow: ellipsis;
    display: -webkit-box;
    -webkit-line-clamp: 3;
    -webkit-box-orient: vertical;
}

.clearfix{
  zoom: 1;
}
.clearfix:after{
  display: block;
  content: '';
  clear: both
}

/* 绝对定位方式且已知宽高 */
{
    position: absolute;
    top: 50%;
    left: 50%;
    margin-top: -3em;
    margin-left: -7em;
    width: 14em;
    height: 6em;
}
/* 绝对定位 ＋ 未知宽高 ＋ translate */
{
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);/*  需要补充浏览器前缀 */
}
/* flex 轻松搞定水平垂直居中( 未知宽高)} */
{
    display: flex;
    align-items: center;
    justify-content: center;
}