Customize Woocommerce ‘Checkout’ page using CSS

Change background color of ‘Place order button’

button#place_order { color: #101010 !important; background-color: #FFD500; }

The ‘color’ code would be the color of the text, and ‘background-color’ would change the BG.

Change Woocommerce messages color (normally blue)

 /* Normally Blue */
.woocommerce-info {
font-weight: 600;
font-family: montserrat;
font-size: 15px;
color:#000;
background-color: #FF400;
border-width:
5px;
border-color: #FFC400;
}

Change font name, size, color, and other things mentioned according to your needs

Change Woocommerce messages icon color

.woocommerce-info::before {
color: #000;
}