section#controls {
    font-family: monospace;
}

#startBtn {
    cursor: pointer;
    min-width: 7ch;
}

section#controls span {
    border-bottom: 4px solid white;
    display: inline-block;
    background: #eef;
    min-height: 1em;
}

section#controls span:empty::before {
    content: '\00a0';
}   

#note1, #note2 {
    min-width: 3ch;
}

#freq1, #freq2 {
    min-width: 7ch;
}

#interval {
    min-width: 14ch;
}

#semitones {
    min-width: 12ch;
}

#feeling {
    background: #efe !important;
    min-width: 11ch;
}

#visualizer {
    display: block;
    width: 100%;
    
    height: 40px;
    background: #eef;
}