css-边框
边框样式
dotted:点线
dashed:虚线
solid:实线
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border:1px solid red; (顺序：上，右，下，左)
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border-top:1px solid red;
border-top-width:1px;
border-top-style:solid;
border-top-color: red;
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border-right:1px solid red;
border-right-width:1px;
border-right-style:solid;
border-right-color: red;
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border-bottom:1px solid red;
border-bottom-width:1px;
border-bottom-style:solid;
border-bottom-color: red;
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border-left:1px solid red;
border-left-width:1px;
border-left-style:solid;
border-left-color: red;
