.container {
    background-color: #fff;
    padding: 30px;
    border-radius: 10px;
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
    max-width: 800px;
    width: 600px;
}

h1 {
    text-align: center;
    color: #333;
}

/* --- Controls --- */
.controls {
    display: flex;
    gap: 15px;
    align-items: center;
    justify-content: center;
    margin-bottom: 20px;
    padding: 10px;
    background-color: #e9ecef;
    border-radius: 5px;
}

#target-select, #start-game {
    padding: 8px 15px;
    border-radius: 5px;
    border: 1px solid #ccc;
}

#start-game {
    background-color: #007bff;
    color: white;
    cursor: pointer;
    transition: background-color 0.3s;
}

#start-game:hover {
    background-color: #0056b3;
}

/* --- Game Area --- */
.game-area {
    border: 2px solid #ccc;
    padding: 20px;
    border-radius: 8px;
    margin-bottom: 20px;
}

.target-display, .score-board {
    font-size: 1.2em;
    font-weight: bold;
    margin-bottom: 10px;
    text-align: center;
}

#target-number {
    color: #dc3545;
}

#correct-count {
    color: #28a745;
}

.current-equation {
    margin-bottom: 15px;
}

#equation-display {
    width: 100%;
    padding: 10px;
    font-size: 1.5em;
    text-align: right;
    border: 2px solid #5cb85c;
    border-radius: 5px;
    box-sizing: border-box;
    background-color: #fff;
}

.board {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    margin-bottom: 15px;
}

.board button {
    padding: 15px 0;
    font-size: 1.2em;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    transition: background-color 0.2s;
}

.board .number {
    background-color: #f0ad4e;
    color: white;
}
.board .number:hover {
    background-color: #ec971f;
}

.board .operator {
    background-color: #5cb85c;
    color: white;
}
.board .operator:hover {
    background-color: #449d44;
}

.actions {
    display: flex;
    justify-content: space-between;
    gap: 10px;
}

#evaluate-btn, #backspace-btn, #clear-btn { /* ADDED #backspace-btn */
    flex-grow: 1;
    padding: 10px;
    font-size: 1.1em;
    border: none;
    border-radius: 5px;
    cursor: pointer;
}


#backspace-btn { /* NEW STYLE */
    background-color: #ffc107; /* Warning yellow */
    color: #333;
}

#evaluate-btn {
    background-color: #007bff;
    color: white;
}
#evaluate-btn:disabled {
    background-color: #a0c3e6;
    cursor: not-allowed;
}
#clear-btn {
    background-color: #dc3545;
    color: white;
}

.feedback-message {
    text-align: center;
    margin-top: 15px;
    font-weight: bold;
}

.success {
    color: #28a745;
}

.error {
    color: #dc3545;
}

/* --- History --- */
.history-area h2 {
    border-bottom: 2px solid #ccc;
    padding-bottom: 5px;
    margin-bottom: 10px;
}

#history-list {
    list-style-type: none;
    padding: 0;
    max-height: 200px;
    overflow-y: auto;
    border: 1px solid #eee;
    padding: 10px;
    border-radius: 5px;
}

#history-list li {
    padding: 5px 0;
    border-bottom: 1px dotted #ccc;
    font-size: 1.1em;
}
#history-list li:last-child {
    border-bottom: none;
}
.correct-entry {
    color: #28a745;
    font-weight: bold;
}
.incorrect-entry {
    color: #dc3545;
    opacity: 0.7;
}