The phrase "seamlessly smooth" is correct and can be used in written English.
You can use it to describe something that proceeds without any disruption, flaw, or interruption. For example: The presentation went off without a hitch--the transitions between speakers were seamless and smooth.
Now the excess energy was pared away; his performances were simple and understated and seamlessly smooth.
The writing is seamlessly smooth but never ostentatious, pushing story to the fore.
Scientists from the Massachusetts Institute of Technology and Harvard say that the material they've developed can seamlessly smooth the appearance of wrinkles and sagging under the eye.
All the themes are intimately related, the gearing between the sections is seamlessly smooth, and the tonal plan starkly simple; Sibelius's technique is pared down to its raw essentials.
The concourse is gloriously streamlined; there is a sense of flow here, fast yet relaxed, ultra-modern and seamlessly smooth, that matches and mirrors the design and ambition of the trains the station serves.
If there's one thing for which to praise Toyota, it's how seamlessly smooth the company makes all of its cars.
The resultant concatenated H/M subbands, upon inverse DWT, results the required seamlessly smoothed image.
I mean, she has a wonderful voice that can oscillate almost seamlessly from smooth and tender, to razored and barbed and husky.
While some moments may have been a bit deep for the casual passerby, Jamie seamlessly crafted a smooth set that was best consumed as a complete package.
I watch the videos without sound, and relish the way icing is smoothed seamlessly over spongey loaves, how colors mingle and mix, how at the end there is a beautiful dessert.
Yet when you find the right fit, when there is a great relationship, it makes things run smooth and seamlessly.
