:root {
    --bg-color: #ffffff;
    --text-color: #000000;
    --primary-color: #000000;
    --secondary-color: #555555;
    --border-color: #000000;
    --input-bg: #ffffff;
    --card-bg: #f5f5f5;
}

[data-theme="dark"] {
    --bg-color: #000000;
    --text-color: #ffffff;
    --primary-color: #ffffff;
    --secondary-color: #aaaaaa;
    --border-color: #ffffff;
    --input-bg: #000000;
    --card-bg: #1a1a1a;
}

body {
    background-color: var(--bg-color);
    color: var(--text-color);
    font-family: 'Inter', sans-serif; /* Assuming Inter or system font */
    margin: 0;
    padding: 0;
    line-height: 1.6;
    transition: background-color 0.3s, color 0.3s;
}

.container {
    max-width: 800px;
    margin: 0 auto;
    padding: 2rem;
}

h1, h2, h3 {
    font-weight: 700;
    letter-spacing: -0.05em;
    margin-bottom: 1rem;
}

a {
    color: var(--primary-color);
    text-decoration: underline;
    text-underline-offset: 4px;
}

button, .btn {
    background-color: var(--primary-color);
    color: var(--bg-color);
    border: 2px solid var(--primary-color);
    padding: 0.75rem 1.5rem;
    font-weight: 600;
    cursor: pointer;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    font-size: 0.9rem;
    transition: transform 0.1s;
}

button:active, .btn:active {
    transform: scale(0.98);
}

input {
    background-color: var(--input-bg);
    color: var(--text-color);
    border: 2px solid var(--border-color);
    padding: 0.75rem;
    width: 100%;
    margin-bottom: 1rem;
    box-sizing: border-box;
    font-size: 1rem;
}

.card {
    background-color: var(--card-bg);
    border: 1px solid var(--border-color);
    padding: 1.5rem;
    margin-bottom: 1rem;
}

.flex { display: flex; }
.justify-between { justify-content: space-between; }
.items-center { align-items: center; }
.gap-4 { gap: 1rem; }
.mb-4 { margin-bottom: 1rem; }
.mt-4 { margin-top: 1rem; }
.hidden { display: none; }