:root {
    --primary-red: #b32424;
    --bg-gray: #f8f9fa;
    --border-color: #e0e0e0;
}

body { font-family: 'PingFang TC', sans-serif; background: var(--bg-gray); margin: 0; padding: 20px; }

.container { max-width: 800px; margin: 0 auto; }

.card { 
    background: #fff; 
    border-radius: 16px; 
    padding: 40px; 
    box-shadow: 0 4px 20px rgba(0,0,0,0.05); 
}

.section-header { display: flex; align-items: center; margin-bottom: 20px; }
.step-num { 
    background: var(--primary-red); color: white; 
    width: 28px; height: 28px; border-radius: 50%; 
    display: flex; justify-content: center; align-items: center; 
    margin-right: 12px; font-weight: bold;
}

/* Responsive Grid */
.grid-4, .grid-3, .grid-2 { display: grid; gap: 10px; margin-bottom: 15px; }
.grid-4 { grid-template-columns: repeat(auto-fit, minmax(120px, 1fr)); }
.grid-3 { grid-template-columns: repeat(auto-fit, minmax(150px, 1fr)); }
.grid-2 { grid-template-columns: 1fr 1fr; }

/* Buttons & Inputs */
.amt-btn, .pay-box {
    border: 1px solid var(--border-color);
    padding: 15px; border-radius: 8px; background: none; cursor: pointer;
    text-align: center; transition: 0.3s;
}

.amt-btn.active, .pay-option input:checked + .pay-box {
    border-color: var(--primary-red); background: var(--primary-red); color: white;
}

.input-field {
    width: 100%; padding: 12px; border: 1px solid var(--border-color);
    border-radius: 8px; box-sizing: border-box; margin-bottom: 10px;
}

.total-bar {
    background: #fff5f5; padding: 20px; border-radius: 8px;
    display: flex; justify-content: space-between; align-items: center;
    margin: 30px 0;
}

.total-amt { color: var(--primary-red); font-size: 24px; font-weight: bold; }

.submit-btn {
    width: 100%; background: var(--primary-red); color: white;
    border: none; padding: 18px; border-radius: 8px; font-size: 18px; cursor: pointer;
}

/* Mobile Tweaks */
@media (max-width: 600px) {
    .grid-2 { grid-template-columns: 1fr; }
    .card { padding: 20px; }
}