/* W3.CSS - bản rút gọn tương thích */
.w3-button {
    display: inline-block;
    padding: 8px 16px;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    text-decoration: none;
    font-size: 14px;
    color: #fff;
    background: #333;
    transition: opacity 0.2s;
}
.w3-button:hover { opacity: 0.75; color: #fff; text-decoration: none; }
.w3-red { background: #c1121f !important; }
.w3-green { background: #0a7d2f !important; }
.w3-blue { background: #1d6fa5 !important; }
.w3-gray { background: #64748b !important; }
.w3-small { font-size: 12px; padding: 5px 10px; }
.w3-large { font-size: 18px; padding: 12px 24px; }
.w3-block { display: block; width: 100%; }
.w3-center { text-align: center; }
.w3-margin { margin: 16px; }
.w3-padding { padding: 8px 16px; }
.w3-hide { display: none !important; }
.w3-card { box-shadow: 0 2px 5px rgba(0, 0, 0, 0.16); }
.w3-round { border-radius: 4px; }