What does it mean? I tried but still stuck

input[type=“submit”] {
display: block;
width: 60%;
min-width: 300px;
margin-top: 1em;
margin-bottom: 1em;
height: 2em;
font-size: 1.1rem;
background-color: #3b3b4f;
border-color: white;
}
I keep getting the following hint:
“You should use the existing margin property to include 1em on the top and bottom.”

It means if there was already a margin property then you should use it to add a 1em top/bottom margin and not add margin-top and margin-bottom properties.