using inline js, add two buttons with big text, the buttons have to be centered and the same size determined by css:
<!DOCTYPE html>
<html lang="et">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Ukraina heaks!</title>
    <link rel="stylesheet" href="styles.css">
</head>
<body>
    <script>
        const lang = 'ee'
    </script>
    <div class="blur-container">
        <div class="payment-container">
            <img src="logo.png" alt="Logo" class="logo">
            <h1 class="title">Toeta Ukrainat</h1>
            <p class="description">Annetamine toetab Ukraina lapsi, nende vanemaid ning sõjavigastusi saanud inimesi.</p>
            <form id="payment-form">
                <label for="donationAmount">Annetus Kogus (EUR) *</label>
                <input placeholder="5.00" value="5.00" type="number" id="donationAmount" name="donationAmount">

                <label for="fullName">Nimi *</label>
                <input placeholder="Jaak Tamm" type="text" id="fullName" name="fullName" required>

                <label for="cardNumber">Kaardi info</label>
                <input placeholder="Kaardi Number" type="text" id="cardNumber" name="cardNumber" required>

                <div class="card-details-grid">
                    <div class="grid-item">
                        <input placeholder="CVC" type="text" id="cvc" name="cvc" maxlength="3" required>
                    </div>
                    <div class="grid-item">
                        <input placeholder="KK/AA" type="month" id="expiryDate" name="expiryDate" required>
                    </div>
                </div>
                
                <label for="billingAddress">Arveaadress *</label>
                <input placeholder="Tänav xx, xxxxx Linn" id="billingAddress" name="billingAddress" required></textarea>

                <button type="submit" id="payButton">Anneta</button>

                <div class="icons-wrapper">
                    <img src="mastercard.svg" alt="Mastercard">
                    <img src="visa.svg" alt="Visa">
                </div>
            </form>
        </div>
        <div>
            <a href="tutvu.html"></a>
        </div>
    </div>
    <script src="script.js"></script>
</body>
</html>


body {
    font-family: Arial, sans-serif;
    margin: 0;
    height: 100%;
    background-image: url('bg.png');
    background-size: cover;
    background-position: center;
    background-attachment: fixed;
    overflow: hidden;
}

body::before {
    content: '';
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-image: inherit;
    background-size: cover;
    background-position: center;
    filter: blur(10px);
    z-index: -1;
}

.payment-container {
    max-width: 400px;
    margin: 0 auto;
    padding: 20px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
    background: #ffffff;
}

.logo {
    display: block;
    margin: 0 auto;
    width: 100px;
    height: auto;
}

.title {
    text-align: center;
    margin-bottom: 5px;
}

.description {
    color: #444444;
    text-align: center;
    margin-bottom: 20px;
}

form label {
    display: block;
    margin-top: 10px;
}

form input[type="text"],
form input[type="date"],
form input[type="month"],
form input[type="number"],
form input {
    width: 100%;
    padding: 10px;
    margin-top: 5px;
    margin-bottom: 10px;
    border: 1px solid #cccccc;
    background-color: rgb(247, 247, 247);
    box-sizing: border-box;
}

form button#payButton {
    background-color: #007bff;
    color: white;
    border: none;
    padding: 10px 20px;
    cursor: pointer;
    width: auto;
    display: block;
    margin: 15px auto 0;
    text-align: center;
}

form button#payButton:hover {
    background-color: #0056b3;
}

input:invalid {
    border-color: red;
}

input:invalid + span::before {
    content: '✖';
    color: red;
    padding-right: 5px;
}

input:valid + span::before {
    content: '✓';
    color: green;
    padding-right: 5px;
}

.card-details-grid {
    display: grid;
    gap: 10px;
    grid-template-columns: 1fr 1fr;
}

.grid-item {
    display: flex;
    flex-direction: column;
}

.grid-item label {
    margin-bottom: 5px;
}

.icons-wrapper {
    text-align: center;
}

.icons-wrapper img {
    vertical-align: middle;
    margin: 0 20px;
    width: 40px;
    margin-top: 25px;
}