* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 20px;
}

.container {
    background: white;
    border-radius: 20px;
    padding: 40px;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
    max-width: 500px;
    width: 100%;
}

h1 {
    color: #333;
    margin-bottom: 30px;
    text-align: center;
    font-size: 28px;
}

form {
    display: flex;
    flex-direction: column;
    gap: 20px;
}

label {
    color: #555;
    font-weight: 600;
    margin-bottom: 5px;
}

select, input {
    padding: 12px 15px;
    border: 2px solid #e0e0e0;
    border-radius: 8px;
    font-size: 16px;
    transition: border-color 0.3s;
}

select:focus, input:focus {
    outline: none;
    border-color: #667eea;
}

button {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    padding: 15px;
    border: none;
    border-radius: 8px;
    font-size: 18px;
    font-weight: 600;
    cursor: pointer;
    transition: transform 0.2s, box-shadow 0.2s;
    margin-top: 10px;
}

button:hover {
    transform: translateY(-2px);
    box-shadow: 0 5px 20px rgba(102, 126, 234, 0.4);
}

button:active {
    transform: translateY(0);
}

#result {
    margin-top: 30px;
    padding: 20px;
    background: #f0f7ff;
    border-radius: 10px;
    border-left: 4px solid #667eea;
}

#result h2 {
    color: #667eea;
    font-size: 20px;
    margin-bottom: 10px;
}

#result p {
    color: #333;
    font-size: 18px;
    font-weight: 500;
}

#btc-amount {
    color: #667eea;
    font-weight: 700;
    font-size: 20px;
}

.error {
    margin-top: 20px;
    padding: 15px;
    background: #fee;
    border-radius: 8px;
    border-left: 4px solid #f44336;
    color: #c62828;
    font-weight: 500;
}

.hidden {
    display: none;
}

/* Responsive design */
@media (max-width: 600px) {
    .container {
        padding: 25px;
    }
    
    h1 {
        font-size: 24px;
    }
}