css triangle

#triangle {
    width: 0;
    height: 0;
    border-left: 18px solid transparent;
    border-right: 18px solid transparent;
    border-bottom: 30px solid blue;
}

#triangle-up {
  width: 0;
  height: 0;
  border-left: 50px solid transparent;
  border-right: 50px solid transparent;
  border-bottom: 100px solid red;
}

<div class="arrow-up"></div>
<div class="arrow-down"></div>
<div class="arrow-left"></div>
<div class="arrow-right"></div>

.arrow-up {
  width: 0; 
  height: 0; 
  border-left: 5px solid transparent;
  border-right: 5px solid transparent;
  
  border-bottom: 5px solid black;
}

.arrow-down {
  width: 0; 
  height: 0; 
  border-left: 20px solid transparent;
  border-right: 20px solid transparent;
  
  border-top: 20px solid #f00;
}

.arrow-right {
  width: 0; 
  height: 0; 
  border-top: 60px solid transparent;
  border-bottom: 60px solid transparent;
  
  border-left: 60px solid green;
}

.arrow-left {
  width: 0; 
  height: 0; 
  border-top: 10px solid transparent;
  border-bottom: 10px solid transparent; 
  
  border-right:10px solid blue; 
}

/*corner triangles if you want normal triangles look at other answers*/
    #triangle-topleft {
      width: 0;
      height: 0;
      border-top: 100px solid red;
      border-right: 100px solid transparent;
    }
    #triangle-topright {
      width: 0;
      height: 0;
      border-top: 100px solid red;
      border-left: 100px solid transparent;
    }
    #triangle-bottomleft {
      width: 0;
      height: 0;
      border-bottom: 100px solid red;
      border-right: 100px solid transparent;
    }

    #triangle-topright {
      width: 0;
      height: 0;
      border-top: 100px solid red;
      border-left: 100px solid transparent;
    }