**Planning interactive audio UI**

I need to create an `index.html` file that uses `tone.min.js` from the current directory. The goal is to build a user interface featuring a piano keyboard, mouse clicks, and computer key mappings tied to notes like 'z', 's', 'x', etc. I'll make sure to include ADSR envelope controls for sound customization and visual feedback when keys are pressed. It's essential to start the audio context on the first interaction, and I'll write the `index.html` file to the current directory.**Deciding on synth options**

I need to choose between using Tone.Synth or Tone.PolySynth. For polyphony, I'll go with Tone.PolySynth and set it up for 8 voices. I want to implement an ADSR envelope with the synth options, and create keyboard mappings across multiple octaves, which means defining semitone offsets. I'll provide a simple octave shift and create key elements with attributes that denote their note. It’s important to implement both mouse and touch events, giving visual feedback by adding an 'active' class when keys are pressed.**Implementing synth controls**

I need to set the envelope sustain parameter value between 0 and 1 and include controls for oscillator type selection, like sine, triangle, square, and sawtooth. I'll implement the keyboard to trigger notes on keydown and keyup while tracking pressed keys to avoid retriggers. Additionally, I want clickable keys to sustain until mouseup. I’ll also add octave shift buttons and create a structured HTML for controls, including ADSR sliders, oscillator selection, and ensure to start Tone on any user gesture. Edge cases will be handled properly for multi-finger input.**Generating keys for octaves**

I need to compute the keys for a given number of octaves, and it looks like I’ll choose 2 octaves starting from octave 3. This means I'll have 24 semitones but only need 14 white keys. To simplify things, I’ll generate notes based on a scale sequence relative to C, using an array for note names in an octave. For each octave, I’ll produce 12 keys, assigning classes for sharps. Then, I’ll render white keys as the base layer, positioning the black keys on top using CSS. The layout will adjust dynamically.**Computing key positions**

I need to compute the left offsets for the keys, positioning black keys between their neighboring white keys. The common formula suggests that the width of each white key is about 100 divided by the white count, and the black keys are around 60% of the white key width. Instead of float, I think absolute positioning will make this easier. I’ll iterate through the white keys and create their left positions while mapping the black keys accordingly. I’ll construct arrays for the white notes and their corresponding black keys, then implement the necessary JavaScript logic.