:root {
    --background-color: #0b0b10;
    --background-elev-1: rgba(255,255,255,0.04);
    --background-elev-2: rgba(255,255,255,0.06);
    --surface-glass: rgba(255,255,255,0.06);
    --text-color: #f4f6f8;
    --muted-text-color: #a7b0be;
    --border-color: rgba(255,255,255,0.12);
    --interactive-bg: rgba(255,255,255,0.06);
    --accent-color: #7ee787;
    --accent-strong: #56d364;
    --shadow-color: 0 10px 30px rgba(0,0,0,0.45);
    --radius: 14px;
    --radius-sm: 10px;
    --radius-xs: 8px;
    --focus-ring: 0 0 0 2px rgba(126,231,135,0.25), 0 0 0 6px rgba(126,231,135,0.1);
    color-scheme: dark;
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
    background:
        radial-gradient(1200px 600px at 80% -10%, rgba(126, 231, 135, 0.12), transparent 60%),
        radial-gradient(1000px 500px at -10% 20%, rgba(99, 102, 241, 0.10), transparent 55%),
        linear-gradient(180deg, #0b0b10 0%, #0b0b10 100%);
    color: var(--text-color);
    line-height: 1.6;
    padding: 28px;
    min-height: 100vh;
}

.container {
    max-width: 980px;
    margin: 0 auto;
}

.container.centered main {
    min-height: 72vh;
    display: grid;
    place-items: center;
    grid-template-columns: 1fr;
}

.container.centered #output-column {
    display: none !important;
}

.container.centered #input-column {
    width: 100%;
    max-width: 640px;
    margin: 0 auto;
}

@media (min-width: 768px) {
    .container.centered main {
        grid-template-columns: 1fr;
    }
}

header {
    text-align: center;
    margin-bottom: 28px;
}

h1 {
    font-weight: 800;
    font-size: 3rem;
    letter-spacing: -0.03em;
    margin-bottom: 8px;
    background: linear-gradient(180deg, #fff 0%, #c8d1de 100%);
    -webkit-background-clip: text;
    background-clip: text;
    color: transparent;
}

h2 {
    font-weight: 700;
    font-size: 1rem;
    margin-bottom: 18px;
    color: var(--muted-text-color);
    text-transform: uppercase;
    letter-spacing: 0.14em;
}

p {
    color: var(--muted-text-color);
}

.tabs {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 12px;
    position: relative;
    width: 100%;
    max-width: 980px;
    margin: 0 auto 28px;
    padding: 0;
    border: 0;
    border-radius: 0;
    background: transparent;
    box-shadow: none;
}

.tab-btn {
    appearance: none;
    background: linear-gradient(180deg, rgba(255,255,255,0.06), rgba(255,255,255,0.03));
    border: 1px solid var(--border-color);
    color: var(--muted-text-color);
    padding: 10px 16px;
    cursor: pointer;
    font-size: 0.95rem;
    font-weight: 600;
    transition: color 0.2s, background 0.2s, border-color 0.2s, transform 0.2s;
    text-align: center;
    width: auto;
    min-width: 160px;
    height: 42px;
    line-height: 20px;
    border-radius: var(--radius-sm);
    box-shadow: var(--shadow-color);
}

.tab-btn.active {
    color: #ecfff0;
    background: linear-gradient(180deg, rgba(126,231,135,0.24), rgba(126,231,135,0.10));
    border-color: rgba(126,231,135,0.5);
}

.tab-btn.active::after {
    display: none;
}

.tabs .tab-btn + .tab-btn {
    border-left: 0;
}

.tab-btn:hover {
    color: #e8ecf1;
    transform: translateY(-1px);
}

.tab-btn:focus-visible {
    outline: none;
    box-shadow: var(--focus-ring), var(--shadow-color);
}

main {
    display: grid;
    grid-template-columns: 1fr;
    gap: 28px;
}

#input-column {
    transition: transform 0.25s ease, opacity 0.25s ease;
}

.container:not(.centered) #input-column {
    transform: translateY(0);
    opacity: 1;
}

.container.centered #input-column {
    transform: translateY(0);
    opacity: 1;
}

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

.upload-area {
    border: 1px dashed var(--border-color);
    border-radius: var(--radius);
    padding: 70px 24px;
    text-align: center;
    cursor: pointer;
    transition: background-color 0.2s, border-color 0.2s, transform 0.2s;
    background: linear-gradient(180deg, rgba(255,255,255,0.04), rgba(255,255,255,0.02));
    box-shadow: var(--shadow-color);
}

.upload-area:hover {
    background-color: var(--interactive-bg);
    border-color: var(--accent-color);
    transform: translateY(-1px);
}

.tab-content {
    display: none;
}

.tab-content.active {
    display: block;
}

.option-group {
    margin-bottom: 20px;
}

.options {
    padding: 18px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    background: linear-gradient(180deg, rgba(255,255,255,0.04), rgba(255,255,255,0.02));
    box-shadow: var(--shadow-color);
}

label {
    display: flex;
    justify-content: space-between;
    margin-bottom: 10px;
    font-weight: 600;
}

select,
input[type="range"] {
    width: 100%;
    padding: 12px;
    background: linear-gradient(180deg, rgba(255,255,255,0.05), rgba(255,255,255,0.03));
    border: 1px solid var(--border-color);
    color: var(--text-color);
    border-radius: var(--radius-xs);
    font-size: 1rem;
    outline: none;
    box-shadow: inset 0 0 0 1px rgba(255,255,255,0.02);
}

select {
    -webkit-appearance: none;
    -moz-appearance: none;
    appearance: none;
    background: linear-gradient(180deg, rgba(255,255,255,0.05), rgba(255,255,255,0.03)), url("data:image/svg+xml,%3Csvg xmlns=%22http://www.w3.org/2000/svg%22 viewBox=%220 0 24 24%22 fill=%23a7b0be%3E%3Cpath d=%22M7 10l5 5 5-5H7z%22/%3E%3C/svg%3E");
    background-repeat: no-repeat, no-repeat;
    background-position: left top, right 12px center;
    background-size: auto, 16px 16px;
    background-color: rgba(255,255,255,0.04);
    padding-right: 44px;
    cursor: pointer;
}

select option {
    color: #0b0b10;
    background-color: #ffffff;
}

select:focus {
    box-shadow: var(--focus-ring);
}

select::-ms-expand {
    display: none;
}

#compress-format {
    -webkit-appearance: menulist;
    -moz-appearance: menulist;
    appearance: auto;
    background-image: none;
    background-color: rgba(255,255,255,0.06);
    padding-right: 12px;
}

input[type="range"] {
    padding: 0;
    accent-color: var(--accent-color);
}

select:focus,
input[type="range"]:focus {
    box-shadow: var(--focus-ring);
}

.result-preview {
    text-align: center;
    padding: 22px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    background: linear-gradient(180deg, rgba(255,255,255,0.04), rgba(255,255,255,0.02));
    box-shadow: var(--shadow-color);
}

#resultImage {
    max-width: 100%;
    max-height: 240px;
    margin: 0 auto 16px;
    display: none;
    border-radius: var(--radius-xs);
}

#fileInfo {
    color: var(--muted-text-color);
    font-size: 0.95rem;
}

.button-group {
    display: flex;
    gap: 12px;
}

button {
    background: linear-gradient(180deg, var(--accent-color), var(--accent-strong));
    color: #0a0f0a;
    border: none;
    padding: 14px 22px;
    font-size: 1rem;
    border-radius: 12px;
    cursor: pointer;
    transition: transform 0.15s ease, box-shadow 0.15s ease, filter 0.15s ease, opacity 0.2s;
    width: 100%;
    font-weight: 700;
    box-shadow: 0 8px 18px rgba(86, 211, 100, 0.35);
}

button:hover:not(:disabled) {
    transform: translateY(-1px);
    filter: saturate(1.05);
}

button:focus-visible {
    outline: none;
    box-shadow: var(--focus-ring), 0 8px 18px rgba(86, 211, 100, 0.35);
}

button:disabled {
    opacity: 0.55;
    cursor: not-allowed;
}

footer {
    text-align: center;
    margin-top: 48px;
    padding: 22px 0;
    color: var(--muted-text-color);
}

header p {
    color: var(--muted-text-color);
}

footer a {
    color: var(--accent-color);
    text-decoration: none;
}

footer a:hover {
    text-decoration: underline;
}

/* Responsive design */
@media (min-width: 768px) {
    main {
        grid-template-columns: 1fr 1fr;
    }
}

@media (max-width: 600px) {
    body {
        padding: 14px;
    }
    
    h1 {
        font-size: 2.3rem;
    }
    
    .upload-area {
        padding: 46px 16px;
    }
}