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1.等腰三角形

.isosceles{ 
    width: 0; 
    height: 0; 
    border:30px solid; 
    border-left-color: transparent; 
    border-right-color: transparent; 
    border-top-color: transparent; 
    border-bottom-color: red; 
}

2.直角三角形

.right{ 
    width: 0; 
    height: 0; 
    border:30px solid; 
    border-left: 0; 
    border-right-color: transparent; 
    border-top: 0; 
    border-bottom-color: red; 
}

3.圓

.round{ 
    width: 100px; 
    height: 100px; 
    background-color: red; 
    border-radius:50%;    
}

4.橢圓

.ellipse{ 
    width: 100px; 
    height: 80px; 
    background-color: red; 
    border-radius:50%;    
}