erpnext/www/book-appointment/index.css

.time-slot {
    flex-grow: 1;
    flex : 0 0 calc(16.66% - 20px);
    margin-bottom: 2em;
    margin-left: 0.5em;
    margin-right: 0.5em;
    border-radius: 0.4em;
    cursor: pointer;
    border: 0.5px solid #cccccc;
    min-height: 75px;
    padding: 0.5em 1em;
}

#customer-form{
    border-color: black;
}
#customer-form ::placeholder{
    color: #ddd;
}
#timeslot-container{
	display: flex;
    flex-wrap: wrap;
    justify-content: center;
}

.time-slot:hover {
    background: #ddd;
}

.time-slot.unavailable {
    background: #CBD5E0;
    cursor: not-allowed;
    color: #718096
}

.time-slot.unavailable .text-muted {
    color: #718096
}

.time-slot.selected {
    color: white;
    background: #5e64ff;
}

.time-slot.selected .text-muted {
    color: #EDF2F7 !important;
}