Check out example codes for "css size". It will help you in understanding the concepts better.

Code Example 1

div {
  height: 
200px;
  width: 50%;
  background-color: powderblue;
}

Code Example 2

#myID {
  height: 100px; /* Sets the height */
  width: 200px; /* Sets the width */
}
/* or... */
.myClass {
  height: 220px; /* Sets the height */
  width: 40px; /* Sets the width */
}
/* They both work! */

Code Example 3

squareImage {
  border: 1px solid #ddd;	/* thickness and color of border */
  border-radius: 4px;		/* edge rounding of border */
  width: 150px;				/* width of image (px or % or auto) */
  height: auto;				/* height of image (px or % or auto) */
}

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