:root {
    --c-bg-main: #f4f7f6;
    --c-bg-card: #ffffff;
    --c-text-main: #333333;
    --c-text-sub: #666666;
    --c-border: #e2e8f0;
    --c-accent: #007acc;
    --c-danger: #ef4444;
}

[data-theme="dark"] {
    --c-bg-main: #0f172a;
    --c-bg-card: #1e293b;
    --c-text-main: #f1f5f9;
    --c-text-sub: #94a3b8;
    --c-border: #334155;
    --c-accent: #3b82f6;
    --c-danger: #f87171;
}

body {
    font-family: 'Helvetica Neue', Arial, sans-serif;
    background-color: var(--c-bg-main);
    color: var(--c-text-main);
    margin: 0;
    padding: 0;
    transition: background-color 0.3s ease, color 0.3s ease;
}

.theme-toggle-btn {
    background: transparent;
    border: 1px solid var(--c-border);
    color: var(--c-text-main);
    padding: 4px 10px;
    border-radius: 4px;
    cursor: pointer;
    font-size: 1.2rem;
    transition: background-color 0.2s, box-shadow 0.2s;
    display: inline-flex;
    align-items: center;
    justify-content: center;
}

.theme-toggle-btn:hover {
    background-color: var(--c-bg-card);
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}