:root {
            --bg-color: #121212;
            --text-color: #E0E0E0;
            --primary-color: #4A90E2;
            --red: #D9534F;
            --green: #5CB85C;
            --yellow: #F0AD4E;
            --dark-grey: #2a2a2a;
            --light-grey: #3d3d3d;
        }

        body {
            font-family: 'Roboto Mono', monospace;
            background-color: var(--bg-color);
            color: var(--text-color);
            display: flex;
            justify-content: center;
            align-items: center;
            min-height: 100vh;
            margin: 0;
            text-align: center;
        }

        .container {
            background-color: var(--dark-grey);
            padding: 2rem 3rem;
            border-radius: 15px;
            box-shadow: 0 10px 30px rgba(0, 0, 0, 0.5);
            width: 90%;
            max-width: 500px;
        }

        h1 {
            color: var(--primary-color);
            margin-top: 0;
        }

        .instructions {
            text-align: left;
            background-color: var(--light-grey);
            padding: 0.5rem 1.5rem;
            border-radius: 8px;
            margin-bottom: 2rem;
        }

        .instructions h3 {
            margin-bottom: 0.5rem;
        }

        .instructions ul {
            padding-left: 20px;
            margin-top: 0.5rem;
        }

        .meter {
            margin-bottom: 2rem;
        }

        #frequency-display {
            font-size: 5rem;
            font-weight: 700;
            margin: 1rem 0;
            line-height: 1;
        }

        #status-message {
            font-size: 1.5rem;
            height: 2.5rem;
            font-weight: bold;
            transition: color 0.3s;
        }
        .status-tight { color: var(--red); }
        .status-loose { color: var(--yellow); }
        .status-good { color: var(--green); }
        .status-ideal { color: #61ff61; }

        .gauge-container {
            position: relative;
            height: 40px;
            width: 100%;
            margin-bottom: 1rem;
        }

        .gauge-background {
            width: 100%;
            height: 20px;
            background: linear-gradient(to right, 
                var(--yellow) 0%, 
                var(--yellow) 33.3%, 
                var(--green) 33.3%, 
                var(--green) 66.6%, 
                var(--red) 66.6%, 
                var(--red) 100%);
            border-radius: 10px;
            position: absolute;
            top: 0;
            left: 0;
        }

        #gauge-indicator {
            position: absolute;
            top: -5px;
            left: 0;
            width: 4px;
            height: 30px;
            background-color: white;
            border-radius: 2px;
            transition: left 0.2s ease-out;
            transform: translateX(-2px);
            box-shadow: 0 0 5px rgba(255, 255, 255, 0.7);
        }

        .gauge-labels {
            display: flex;
            justify-content: space-between;
            position: absolute;
            width: 100%;
            top: 25px;
            font-size: 0.8rem;
            color: #888;
        }

        .gauge-labels .ideal {
            font-weight: bold;
            color: var(--text-color);
        }

        button {
            font-family: 'Roboto Mono', monospace;
            background-color: var(--primary-color);
            color: white;
            border: none;
            padding: 1rem 2rem;
            font-size: 1.2rem;
            border-radius: 8px;
            cursor: pointer;
            transition: background-color 0.3s;
            margin-bottom: 1rem;
        }

        button:hover {
            background-color: #357ABD;
        }

        button.listening {
            background-color: var(--red);
        }

        button.listening:hover {
            background-color: #c9302c;
        }

        .specs {
            font-size: 0.9rem;
            color: #aaa;
        }

        .options-container {
            margin-bottom: 1.5rem;
            display: flex;
            justify-content: center;
            align-items: center;
            gap: 10px;
        }

        .options-container label {
            font-size: 1rem;
        }

        #algorithm-select {
            font-family: 'Roboto Mono', monospace;
            background-color: var(--light-grey);
            color: var(--text-color);
            border: 1px solid var(--primary-color);
            border-radius: 5px;
            padding: 0.5rem;
            font-size: 1rem;
            cursor: pointer;
            transition: box-shadow 0.2s;
        }

        #algorithm-select:focus {
            outline: none;
            box-shadow: 0 0 8px var(--primary-color);
        }

        #algorithm-select:disabled {
            opacity: 0.5;
            cursor: not-allowed;
        }