:root {
    --topbar-h: 3rem;
    --bg: #1a1d23;
    --bg-input: #0f1115;
    --border: #2e3340;
    --text: #e8eaed;
    --muted: #9aa0a6;
    --accent: #3d8bfd;
    --accent-hover: #5a9dff;
}

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

html, body {
    height: 100%;
    overflow: hidden;
    font-family: "Segoe UI", system-ui, sans-serif;
    background: var(--bg);
    color: var(--text);
}

.topbar {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    height: var(--topbar-h);
    padding: 0 0.75rem;
    background: var(--bg);
    border-bottom: 1px solid var(--border);
}

.topbar input[type="url"],
.topbar input[type="text"] {
    flex: 1;
    min-width: 0;
    height: 2rem;
    padding: 0 0.6rem;
    border: 1px solid var(--border);
    border-radius: 4px;
    background: var(--bg-input);
    color: var(--text);
    font-size: 0.875rem;
}

.topbar input[type="number"] {
    width: 100px;
    flex-shrink: 0;
    height: 2rem;
    padding: 0 0.4rem;
    border: 1px solid var(--border);
    border-radius: 4px;
    background: var(--bg-input);
    color: var(--text);
    font-size: 0.875rem;
    text-align: center;
}

.topbar input:focus {
    outline: none;
    border-color: var(--accent);
}

.btn {
    flex-shrink: 0;
    height: 2rem;
    padding: 0 0.85rem;
    border: 1px solid var(--border);
    border-radius: 4px;
    background: var(--accent);
    color: #fff;
    font-size: 0.8125rem;
    font-weight: 600;
    letter-spacing: 0.02em;
    cursor: pointer;
}

.btn:hover {
    background: var(--accent-hover);
}

.btn:active {
    transform: translateY(1px);
}

.nav-group {
    display: flex;
    flex-shrink: 0;
    border: 1px solid var(--border);
    border-radius: 4px;
    overflow: hidden;
}

.nav-group .btn-nav {
    width: 2.25rem;
    height: calc(2rem - 2px);
    padding: 0;
    border: none;
    border-radius: 0;
    background: var(--bg-input);
    color: var(--text);
    font-size: 1rem;
    line-height: 1;
    cursor: pointer;
}

.nav-group .btn-nav + .btn-nav {
    border-left: 1px solid var(--border);
}

.nav-group .btn-nav:hover {
    background: #252930;
    color: #fff;
}

.viewer {
    position: relative;
    height: calc(100% - var(--topbar-h));
    width: 100%;
    background: #2a2d33;
}

.viewer-placeholder {
    position: absolute;
    inset: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    pointer-events: none;
    color: rgba(255, 255, 255, 0.35);
    font-size: clamp(2rem, 6vw, 4rem);
    font-weight: 600;
    letter-spacing: 0.04em;
    user-select: none;
}

.viewer.is-loaded .viewer-placeholder {
    display: none;
}

.viewer iframe {
    display: block;
    width: 100%;
    height: 100%;
    border: 0;
    background: transparent;
    visibility: hidden;
}

.viewer.is-loaded iframe {
    visibility: visible;
    background: #fff;
}