keyframes spin 100 transform rotate 360deg spinner width 30px height 3

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@keyframes spin {
100% {
transform: rotate(360deg);
}
}
.spinner {
width: 30px;
height: 30px;
border: 6px solid #000;
border-left-color: #333;
border-right-color: transparent;
border-bottom-color: #555;
border-radius: 100%;
animation: spin 600ms infinite linear;
}
<div class="spinner"></div>