:root {
    --bg-primary: #121212;
    --bg-secondary: #1e1e1e;
    --bg-tertiary: #2d2d2d;
    --text-primary: #e0e0e0;
    --text-secondary: #b0b0b0;
    --accent: #bb86fc;
    --accent-secondary: #03dac6;
    --error: #cf6679;
    --success: #4caf50;
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    padding-bottom: 50px;
}

header {
    background-color: var(--bg-secondary);
    padding: 2rem;
    text-align: center;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.3);
}

h1 {
    font-size: 2.5rem;
    margin-bottom: 0.5rem;
}

.subtitle {
    color: var(--text-secondary);
    font-size: 1.2rem;
}

.highlight {
    color: var(--accent);
}

nav {
    background-color: var(--bg-tertiary);
    padding: 1rem 0;
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.3);
}

nav ul {
    display: flex;
    justify-content: center;
    list-style: none;
    flex-wrap: wrap;
}

nav li {
    margin: 0 1rem;
}

nav a {
    color: var(--text-primary);
    text-decoration: none;
    font-weight: 500;
    transition: color 0.3s;
    padding: 0.5rem 1rem;
    border-radius: 4px;
}

nav a:hover {
    color: var(--accent);
    background-color: rgba(187, 134, 252, 0.1);
}

main {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem;
}

.tense-section, .practice-section {
    background-color: var(--bg-secondary);
    border-radius: 8px;
    margin-bottom: 2rem;
    padding: 2rem;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
}

h2 {
    font-size: 2rem;
    margin-bottom: 1.5rem;
    color: var(--accent);
    border-bottom: 2px solid var(--accent);
    padding-bottom: 0.5rem;
}

h3 {
    font-size: 1.5rem;
    margin: 1.5rem 0 1rem;
    color: var(--accent-secondary);
}

.tense-content {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
}

@media (max-width: 768px) {
    .tense-content {
        grid-template-columns: 1fr;
    }
}

ul {
    margin-left: 1.5rem;
}

li {
    margin-bottom: 0.5rem;
}

.tense-explanation, .tense-examples {
    background-color: var(--bg-tertiary);
    padding: 1.5rem;
    border-radius: 8px;
}

.practice-content {
    background-color: var(--bg-tertiary);
    padding: 1.5rem;
    border-radius: 8px;
}

.exercise {
    margin: 1.5rem 0;
}

.exercise-item {
    background-color: var(--bg-secondary);
    padding: 1rem;
    border-radius: 6px;
    margin-bottom: 1rem;
}

.answer-box {
    margin-top: 0.5rem;
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
}

.answer {
    color: var(--accent);
    font-weight: bold;
}

.gap-sentence {
    background-color: var(--bg-secondary);
    padding: 1rem;
    border-radius: 6px;
    margin-bottom: 1rem;
}

input[type="text"] {
    background-color: var(--bg-tertiary);
    border: 1px solid var(--text-secondary);
    border-radius: 4px;
    color: var(--text-primary);
    padding: 0.5rem;
    margin: 0 0.25rem;
    width: 200px;
    font-family: inherit;
}

.btn {
    background-color: var(--accent);
    color: #000;
    border: none;
    padding: 0.75rem 1.5rem;
    border-radius: 4px;
    cursor: pointer;
    font-weight: bold;
    font-size: 1rem;
    transition: background-color 0.3s;
    margin-top: 1.5rem;
}

.btn:hover {
    background-color: #a370db;
}

#result {
    margin-top: 1rem;
    padding: 1rem;
    border-radius: 4px;
    font-weight: bold;
}

.correct {
    color: var(--success);
}

.incorrect {
    color: var(--error);
}

footer {
    text-align: center;
    padding: 1.5rem;
    background-color: var(--bg-secondary);
    color: var(--text-secondary);
    position: fixed;
    bottom: 0;
    width: 100%;
}

/* Animations */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.tense-section, .practice-section {
    animation: fadeIn 0.5s ease-out;
}