| m为margin,p为padding(这里省略)。 .w-25 {  width: 25% !important;}
 .w-50 {  width: 50% !important;}
 .w-75 {  width: 75% !important;}
 .w-100 {  width: 100% !important;}
 .h-25 {  height: 25% !important;}
 .h-50 {  height: 50% !important;}
 .h-75 {  height: 75% !important;}
 .h-100 {  height: 100% !important;}
 .mw-100 {  max-width: 100% !important;}
 .mh-100 {  max-height: 100% !important;}
 .m-0 {  margin: 0 !important;}
 .mt-0,.my-0 {  margin-top: 0 !important;}
 .mr-0,.mx-0 {  margin-right: 0 !important;}
 .mb-0 ,.my-0{  margin-bottom: 0 !important;}
 .ml-0,.mx-0 {  margin-left: 0 !important;}
 
 .m-1 {  margin: 0.25rem !important;}
 .mt-1,.my-1 {  margin-top: 0.25rem !important;}
 .mr-1,.mx-1 {  margin-right: 0.25rem !important;}
 .mb-1,.my-1 {  margin-bottom: 0.25rem !important;}
 .ml-1,.mx-1 {  margin-left: 0.25rem !important;}
 .m-2 {  margin: 0.5rem !important;}
 .mt-2,.my-2 {  margin-top: 0.5rem !important;}
 .mr-2,.mx-2 {  margin-right: 0.5rem !important;}
 .mb-2,.my-2 {  margin-bottom: 0.5rem !important;}
 .ml-2,.mx-2 {  margin-left: 0.5rem !important;}
 .m-3 {  margin: 1rem !important;}
 .mt-3,.my-3 {  margin-top: 1rem !important;}
 .mr-3,.mx-3 {  margin-right: 1rem !important;}
 .mb-3,.my-3 {  margin-bottom: 1rem !important;}
 .ml-3,.mx-3 {  margin-left: 1rem !important;}
 .m-4 {  margin: 1.5rem !important;}
 .mt-4,.my-4 {  margin-top: 1.5rem !important;}
 .mr-4,.mx-4 {  margin-right: 1.5rem !important;}
 .mb-4,.my-4 {  margin-bottom: 1.5rem !important;}
 .ml-4,.mx-4 {  margin-left: 1.5rem !important;}
 .m-5 {  margin: 3rem !important;}
 .mt-5,.my-5 {  margin-top: 3rem !important;}
 .mr-5,.mx-5 {  margin-right: 3rem !important;}
 .mb-5,.my-5 {  margin-bottom: 3rem !important;}
 .ml-5,.mx-5 {  margin-left: 3rem !important;}
 
 xy轴的利用
 mx-0{x轴左右:margin-left:0;margin-right:0}
 my-0{y轴左右:margin-top:0;margin-bottom:0}
 
 手机等设备尽量用rem,em
 
 关于文中的!important的重要提示:如何和何时使用CSS的!important
 
 
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