.progress-btn { position: relative; overflow: hidden; border: none; }
.progress-btn .progress-fill {
    position: absolute; top: 0; left: 0; bottom: 0;
    background: rgba(0, 0, 0, 0.15); width: 0%;
    transition: width 0.1s linear; z-index: 1;
}
body.dark-mode .progress-btn .progress-fill { background: rgba(255, 255, 255, 0.2); }
.progress-btn span { position: relative; z-index: 2; pointer-events: none; }