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

body {
    font-family: 'Roboto', sans-serif;
    background-color: #f5f7fa;
    color: #2d3748;
    line-height: 1.6;
    height: 100vh;
    overflow: hidden;
}

/* Screen Container */
.screen {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    padding: 20px;
    transition: all 0.3s ease;
}

.hidden {
    display: none !important;
}

.container {
    background: white;
    border-radius: 12px;
    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.1);
    padding: 2.5rem;
    max-width: 600px;
    width: 100%;
    text-align: center;
}

/* Typography */
h1 {
    color: #2b6cb0;
    margin-bottom: 1.5rem;
    font-size: 2rem;
}

.instructions {
    color: #4a5568;
    margin-bottom: 2rem;
    font-size: 1.1rem;
}

/* Buttons */
.btn {
    background-color: #4299e1;
    color: white;
    border: none;
    padding: 0.8rem 2rem;
    font-size: 1.1rem;
    border-radius: 6px;
    cursor: pointer;
    transition: all 0.3s ease;
    font-weight: 500;
    margin: 0.5rem;
}

.btn:hover {
    background-color: #3182ce;
    transform: translateY(-2px);
}

.btn:active {
    transform: translateY(0);
}

/* Game Screen */
.score-container {
    display: flex;
    justify-content: space-around;
    margin-bottom: 2rem;
    font-size: 1.1rem;
    font-weight: 500;
    color: #4a5568;
}

.problem {
    font-size: 2.5rem;
    font-weight: 700;
    margin: 2rem 0;
    min-height: 4rem;
    color: #2b6cb0;
    word-wrap: break-word;
}

.input-container {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 1rem;
    margin: 2rem 0;
}

.answer-input {
    font-size: 1.8rem;
    padding: 0.8rem 1.2rem;
    width: 120px;
    text-align: center;
    border: 2px solid #e2e8f0;
    border-radius: 6px;
    transition: all 0.3s ease;
}

.answer-input:focus {
    outline: none;
    border-color: #4299e1;
    box-shadow: 0 0 0 3px rgba(66, 153, 225, 0.2);
}

/* Feedback */
.feedback {
    min-height: 1.8rem;
    margin: 1.5rem 0;
    font-size: 1.2rem;
    font-weight: 500;
}

.correct {
    color: #38a169;
}

.incorrect {
    color: #e53e3e;
}

/* Responsive Design */
@media (max-width: 480px) {
    .container {
        padding: 1.5rem;
    }
    
    h1 {
        font-size: 1.8rem;
    }
    
    .problem {
        font-size: 2rem;
        margin: 1.5rem 0;
    }
    
    .input-container {
        flex-direction: column;
    }
    
    .answer-input {
        font-size: 1.5rem;
        width: 100%;
        max-width: 200px;
    }
    
    .btn {
        width: 100%;
        max-width: 200px;
    }
}