:root {
    --primary-color: #6366f1; 
    --primary-hover: #4f46e5; 
    --bg-main: #f8fafc; 
    --bg-subtle: #f1f5f9; 
    --card-bg: #ffffff; 
    --card-border: #e5e7eb; 
    --text-dark: #1e293b; 
    --text-light: #475569; 
    --success: #10b981; 
    --danger: #ef4444; 
    --shadow-color: rgba(99, 102, 241, 0.1); 
    --shadow-lg-color: rgba(99, 102, 241, 0.2);
    --transition-smooth: all 0.35s cubic-bezier(0.25, 1, 0.5, 1);
}

[data-theme="dark"] {
    --primary-color: #818cf8; 
    --primary-hover: #a78bfa; 
    --bg-main: #0f172a; 
    --bg-subtle: #1e293b; 
    --card-bg: #111827; 
    --card-border: #374151; 
    --text-dark: #f3f4f6; 
    --text-light: #cbd5e1; 
    --shadow-color: rgba(0, 0, 0, 0.3); 
    --shadow-lg-color: rgba(0, 0, 0, 0.4);
}

/* GPU HARDWARE ACCELERATION RULES */
.app-container, .screen, .tool-container, .before-after-container {
    transform: translateZ(0);
    backface-visibility: hidden;
    will-change: min-height, transform, opacity;
}

/* --- CORE KEYFRAMES --- */
@keyframes gradientFlow { 
    0% { background-position: 0% 50%; } 
    50% { background-position: 100% 50%; } 
    100% { background-position: 0% 50%; } 
}

@keyframes shine {
    100% { left: 125%; }
}

@keyframes progressStripes {
    0% { background-position: 0 0; }
    100% { background-position: 40px 0; }
}

@keyframes fadeInUpCustom {
    from {
        opacity: 0;
        transform: translateY(12px) scale(0.99);
    }
    to {
        opacity: 1;
        transform: translateY(0) scale(1);
    }
}

@keyframes popSelect {
    0% { transform: scale(1); }
    50% { transform: scale(1.04); }
    100% { transform: scale(1); }
}

@keyframes heartbeat {
    0% { box-shadow: 0 0 0 0 rgba(99, 102, 241, 0.4); }
    70% { box-shadow: 0 0 0 8px rgba(99, 102, 241, 0); }
    100% { box-shadow: 0 0 0 0 rgba(99, 102, 241, 0); }
}

/* Background Animated Layer */
body::before {
    content: ''; position: fixed; top: 0; left: 0; right: 0; bottom: 0; z-index: -1;
    background: linear-gradient(-45deg, #e0e7ff, #c7d2fe, #a5b4fc, #818cf8);
    background-size: 400% 400%;
    animation: gradientFlow 25s ease infinite;
    transition: opacity 0.5s ease;
    will-change: background-position;
}

[data-theme="dark"] body::before {
    background: linear-gradient(-45deg, #1e293b, #334155, #0f172a, #312e81);
    background-size: 400% 400%;
}

body { 
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif; 
    background-color: var(--bg-main); 
    color: var(--text-dark); 
    transition: background-color 0.3s ease, color 0.3s ease; 
    text-rendering: optimizeLegibility;
}

.app-container { 
    background-color: var(--card-bg); 
    box-shadow: 0 20px 40px -15px var(--shadow-color); 
    border-radius: 1.5rem; 
    border: 1px solid var(--card-border); 
    overflow: hidden; 
    transition: min-height 0.3s cubic-bezier(0.25, 1, 0.5, 1), background-color 0.3s, border-color 0.3s;
}

.screen { 
    opacity: 1;
    transform: translateY(0) scale(1);
}

.screen:not(.hidden) {
    animation: fadeInUpCustom 0.35s cubic-bezier(0.16, 1, 0.3, 1) forwards;
}

.screen.hidden { 
    position: absolute; 
    top: 0; 
    left: 0; 
    right: 0; 
    opacity: 0; 
    pointer-events: none; 
    transform: translateY(12px) scale(0.99); 
}

/* Action Buttons */
.upload-button { 
    position: relative;
    background: linear-gradient(135deg, var(--primary-color), var(--primary-hover)); 
    color: white; 
    padding: 0.85rem 1.75rem; 
    border-radius: 9999px; 
    font-weight: 600; 
    display: inline-flex; 
    align-items: center; 
    gap: 0.5rem; 
    box-shadow: 0 4px 15px -3px var(--shadow-color); 
    transition: var(--transition-smooth);
    overflow: hidden;
}

.upload-button::after {
    content: '';
    position: absolute;
    top: 0;
    left: -50%;
    width: 30%;
    height: 100%;
    background: linear-gradient(to right, rgba(255, 255, 255, 0) 0%, rgba(255, 255, 255, 0.3) 50%, rgba(255, 255, 255, 0) 100%);
    transform: skewX(-25deg);
}

.upload-button:hover::after {
    animation: shine 0.8s ease-in-out;
}

.upload-button:hover { 
    transform: translateY(-2px) scale(1.01); 
    box-shadow: 0 8px 25px -5px var(--shadow-lg-color); 
}

.start-btn {
    animation: heartbeat 2.2s infinite;
}

.download-btn { 
    background: linear-gradient(135deg, var(--success), #14b8a6); 
    box-shadow: 0 4px 20px -3px rgba(16, 185, 129, 0.3); 
}

.secondary-btn { 
    background-color: var(--bg-subtle); 
    border: 1px solid var(--card-border); 
    color: var(--text-dark); 
    transition: var(--transition-smooth);
}

.secondary-btn:hover {
    background-color: var(--card-border);
    transform: translateY(-1px);
}

.logo-image {
    transition: transform 0.4s cubic-bezier(0.25, 1, 0.5, 1);
}
header a:hover .logo-image {
    transform: scale(1.05) rotate(3deg);
}

#themeToggleBtn i {
    transition: transform 0.5s cubic-bezier(0.34, 1.56, 0.64, 1);
}
#themeToggleBtn:hover i {
    transform: scale(1.1) rotate(15deg);
}

.quality-value {
    display: inline-block;
    font-variant-numeric: tabular-nums;
    transition: transform 0.1s ease;
}

/* Tool Cards */
.tool-choice-card { 
    border: 1px solid var(--card-border); 
    border-radius: 1.25rem;
    transition: transform 0.3s cubic-bezier(0.25, 1, 0.5, 1), border-color 0.3s, box-shadow 0.3s; 
    background-color: var(--card-bg); 
    display: block; 
}

.tool-choice-card:hover { 
    transform: translateY(-4px) scale(1.005); 
    border-color: var(--primary-color); 
    box-shadow: 0 15px 25px -10px var(--shadow-lg-color); 
}

.icon-sync, .icon-compress, .icon-expand, .icon-copyright {
    display: inline-block;
    transition: var(--transition-smooth);
}

.drop-zone {
    transition: var(--transition-smooth);
}
.drop-zone:hover {
    border-color: var(--primary-color) !important;
    background-color: rgba(99, 102, 241, 0.02) !important;
}

/* 3D Flip Card */
.format-selector {
    perspective: 1000px;
}

.format-card-container {
    perspective: 1000px;
    height: 110px;
}

.format-card {
    position: relative;
    width: 100%;
    height: 100%;
    transform-style: preserve-3d;
    transition: transform 0.5s cubic-bezier(0.4, 0, 0.2, 1);
    border-radius: 1rem;
}

.format-card.selected {
    animation: popSelect 0.35s ease;
    transform: rotateY(180deg);
}

.card-face {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: 1rem;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    border: 2px solid var(--card-border);
    background-color: var(--card-bg);
}

.card-front {
    color: var(--text-dark);
}

.card-back {
    background: linear-gradient(135deg, var(--primary-color), var(--primary-hover));
    color: white !important;
    transform: rotateY(180deg);
    border-color: var(--primary-color);
}

.card-back i {
    color: white !important;
}

/* Toast */
.toast { 
    position: fixed; 
    bottom: 2rem; 
    left: 50%; 
    transform: translateX(-50%) translateY(120px); 
    background-color: var(--card-bg); 
    color: var(--text-dark); 
    padding: 0.85rem 1.5rem; 
    border-radius: 2rem; 
    box-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.15); 
    z-index: 1000; 
    border: 1px solid var(--card-border); 
    transition: all 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275); 
    opacity: 0; 
}

.toast.show { 
    transform: translateX(-50%) translateY(0); 
    opacity: 1; 
}

/* Progress Bar */
.progress-bar-container { 
    width: 100%; 
    height: 10px; 
    background-color: var(--bg-subtle); 
    border-radius: 999px; 
    overflow: hidden; 
}

.progress-bar-fill { 
    height: 100%; 
    border-radius: 999px; 
    background: linear-gradient(
        45deg, 
        var(--primary-color) 25%, 
        var(--primary-hover) 25%, 
        var(--primary-hover) 50%, 
        var(--primary-color) 50%, 
        var(--primary-color) 75%, 
        var(--primary-hover) 75%
    ); 
    background-size: 40px 40px;
    animation: progressStripes 1.5s linear infinite;
    transition: width 0.3s ease-out; 
}

[data-theme="dark"] .fa-sun { display: none; }
body:not([data-theme="dark"]) .fa-moon { display: none; }

/* Comparison Elements */
.before-after-container { 
    position: relative; 
    width: 100%; 
    height: 100%; 
    margin: auto; 
    aspect-ratio: var(--aspect-ratio, 1/1); 
    overflow: hidden; 
    border-radius: 0.75rem; 
    user-select: none; 
    box-shadow: 0 10px 25px -5px var(--shadow-color);
    cursor: grab;
    background-color: #000;
}

.before-after-container:active {
    cursor: grabbing;
}

.comparison-viewport {
    width: 100%;
    height: 100%;
    position: relative;
    transform-origin: center center;
    transition: transform 0.05s ease-out;
}

.comparison-viewport img { 
    position: absolute; 
    top: 0; 
    left: 0; 
    width: 100%; 
    height: 100%; 
    object-fit: contain; 
    pointer-events: none; 
}

.before-image-clipper { 
    position: absolute; 
    inset: 0; 
    clip-path: inset(0 50% 0 0); 
    transition: clip-path 0.05s ease-out;
}

.before-after-slider { 
    position: absolute; 
    background: #ffffff; 
    z-index: 10; 
    box-shadow: 0 0 8px rgba(0,0,0,0.4);
    transition: left 0.05s ease-out, top 0.05s ease-out;
}

.before-after-container.horizontal-split .before-after-slider {
    top: 0; 
    left: 50%; 
    transform: translateX(-50%); 
    width: 3px; 
    height: 100%; 
    cursor: ew-resize; 
}

.before-after-container.horizontal-split .before-after-slider::before { 
    content: ''; position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%); 
    width: 36px; height: 36px; border: 2.5px solid white; border-radius: 50%; 
    background: rgba(15, 23, 42, 0.7); backdrop-filter: blur(4px); 
    box-shadow: 0 4px 10px rgba(0,0,0,0.3);
}

.before-after-container.horizontal-split .before-after-slider::after { 
    content: '\f337'; font-family: 'Font Awesome 6 Free'; font-weight: 900; color: white; 
    position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%); font-size: 14px;
}

.before-after-container.vertical-split .before-image-clipper {
    clip-path: inset(0 0 50% 0);
}

.before-after-container.vertical-split .before-after-slider {
    top: 50%; 
    left: 0; 
    transform: translateY(-50%); 
    width: 100%; 
    height: 3px; 
    cursor: ns-resize; 
}

.before-after-container.vertical-split .before-after-slider::before { 
    content: ''; position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%); 
    width: 36px; height: 36px; border: 2.5px solid white; border-radius: 50%; 
    background: rgba(15, 23, 42, 0.7); backdrop-filter: blur(4px); 
    box-shadow: 0 4px 10px rgba(0,0,0,0.3);
}

.before-after-container.vertical-split .before-after-slider::after { 
    content: '\f338'; font-family: 'Font Awesome 6 Free'; font-weight: 900; color: white; 
    position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%); font-size: 14px;
}

.results-summary { 
    background-color: var(--bg-subtle); border: 1px solid var(--card-border); padding: 1rem; border-radius: 0.75rem; margin-bottom: 1rem; 
}

.result-card { 
    background-color: var(--card-bg); border: 1px solid var(--card-border); border-radius: 1rem; padding: 1rem; 
    box-shadow: 0 4px 15px -5px var(--shadow-color); transition: var(--transition-smooth); 
}

.result-card:hover { 
    box-shadow: 0 12px 25px -5px var(--shadow-lg-color); transform: translateY(-2px); 
}

.card-thumbnail { 
    width: 64px; height: 64px; object-fit: cover; border-radius: 0.5rem; background-color: var(--bg-subtle); 
    transition: transform 0.3s ease;
}
.result-card:hover .card-thumbnail {
    transform: scale(1.03);
}

.format-badge { 
    display: inline-block; padding: 2px 8px; font-size: 0.7rem; font-weight: 600; border-radius: 999px; 
    background-color: var(--bg-subtle); color: var(--text-light); 
}

.saved-bar-container { 
    height: 6px; background-color: var(--bg-subtle); border-radius: 999px; overflow: hidden; flex-grow: 1; 
}

.saved-bar-fill { 
    height: 100%; background-color: var(--success); border-radius: 999px; 
}

.action-btn-card { 
    background-color: var(--bg-subtle); color: var(--text-dark); border: 1px solid var(--card-border); 
    padding: 0.5rem 0.75rem; border-radius: 0.5rem; font-size: 0.8rem; font-weight: 500; 
    display: inline-flex; align-items: center; gap: 0.3rem; transition: var(--transition-smooth); 
}

.action-btn-card:hover { 
    background-color: var(--primary-color); color: white; border-color: var(--primary-color); 
    transform: translateY(-1px);
}

/* Modals */
.preview-modal { 
    position: fixed; top: 0; left: 0; right: 0; bottom: 0; background-color: rgba(0,0,0,0.6); 
    backdrop-filter: blur(8px); z-index: 1001; display: flex; align-items: center; justify-content: center; 
    opacity: 0; pointer-events: none; transition: opacity 0.3s cubic-bezier(0.25, 0.8, 0.25, 1); 
}

.preview-modal.show { opacity: 1; pointer-events: auto; }

.modal-content { 
    background-color: var(--card-bg); padding: 1.5rem; border-radius: 1.5rem; max-width: 90vw; max-height: 90vh; 
    display: flex; flex-direction: column; gap: 1rem; transform: scale(0.95); transition: transform 0.3s cubic-bezier(0.34, 1.56, 0.64, 1); 
}

.preview-modal.show .modal-content { transform: scale(1); }

.content-page { max-width: 800px; margin: 0 auto; line-height: 1.8; }
.content-page h2 { font-size: 2rem; font-weight: 700; margin-bottom: 1rem; border-bottom: 2px solid var(--primary-color); padding-bottom: 0.5rem; }
.content-page h3 { font-size: 1.5rem; font-weight: 600; margin-top: 2rem; margin-bottom: 1rem; }
.content-page p { margin-bottom: 1rem; color: var(--text-light); }

#card-footer { display: none; text-align: center; padding: 1.5rem; margin-top: 2rem; border-top: 1px solid var(--card-border); }