Why won't this accept my code? I've tried everyway I knew to type it.

"Using the prefix for WebKit-based browsers, create a transition for the border-radius property of .box. Give the transition a duration of 2 seconds, a delay of 1 second, and a timing function that maintains a linear motion."

There's a few areas where you are going wrong. Firstly, you have not used the -webkit prefix as stated in the first portion of the challenge.

Second, when using transition, the order is:

transition: [transition-property] [transition-duration] [transition-timing-function] [transition-delay];

The challenge is asking to transition the border-radius property of .box, so the first portion for transition-property should be set to border-radius. The second is the duration, which the challenge is asking be set to 2s. Jumping ahead it specifies that the transition should "maintain a linear motion" so the transition-timing-function we use is "linear", and finally for the transition delay it asks for 1s. Together you have:

.box {
    border-radius: 15px;
    background: #4682B4;
  -webkit-transition: border-radius 2s linear 1s;
 }

.box:hover {
    background: #F08080;
    border-radius: 50%;
}